Albert Francis Blakeslee

Variations in Datura Due to Changes in Chromosome Number

Two forms with which we ha.vTe recently carried on breeding experiments, the garden flower Portulaca and the jimson weed (Datura Stramnoniumn), are strikingly different in the types of variations which they show. The Porttulaca is procurable in a wide range of color varieties, and is apparently subject to relatively frequent mutations, both seminal and sonmatic, with sectorial and periclinal chimeras a common phenomenon. Sufficient breeding tests have been made to indicate that the varieties of Portulaca are due in large measure at least to gene nmutations. In comparison with Portutlaca, the jimson weed is relatively stable so far as gene mutations are concerned. Despite the large amount of breeding work with this species, both before and since the rediscovery of Mendels law, only the two allelomnorphic pairs of characters, purple vs. white flowers, and spiny vs. smooth capsules, have been identified aside from the pair, tall vs. short stature recently determined by the writer and Avery (3). It is true that certain of our pure lines of Datura differ slightly from others when grown in comparable pedigrees, but the fact remains that so far as sharply contrasting Mendelian characters are concerned, .the jimson weed! is highly stable, while the Portulaca is highly mutable. Our knowledge of changes in chromosome number in other forms is not sufficient o indicate if there is any significance for the present discussion in the difference just mentioned between Portttlaca and Datura. Our interest in Datura began about 1910 or 1911, when the jimsons were used as demonstration material for students in genetics. In 1915 we found our first mutaiit which we ca.lled the Globe fronm the shape of its capsules.

The Assortment of Chromosomes in Triploid Daturas

The present article is the one of a number of proposed papers which will deal with the behavior of the chromnosomes in the different classes, of Datura mutants, the correlation of the chromosomal differences with changes in structural and other characters, and with the ratios in which Mendelian allelomorphs are found in the offspring. The method mainly used in the microscopical examination, and the general principles involved, are given in two papers already in press for THE AMERICAN

The Distribution of Chromosomes in Tetraploid Daturas

(1) The chromosomes at the late prophase and metaphase of the first, or reduction division, in true tetraploid Daturas, are as a rule joined in quadrivalents, which in most cases are formed of two connected pairs. (2) In each of the 79 true tetraploid plants examined there was a certain amount of the 23 + 25 chromosome distribution after the reduction division. This averaged in the most reliable lot of counts, namely, the double groups from 55 sibs, nearly 25 per cent. (3) The distribution of the chromosomes after the reduction division in true tetraploids, in the 467 cells with double groups, agreed closely with the distribution calculated for 35 cases of 2 2 disjunction to 1 case of 3 1 non-disjunction in the quadrivalents. (4) Detachment (elimination) of chromosomes occurred in 2.3 per cent. of the pollen-mother-cells, chiefly (or wholly) at the reduction division. Non-reduction happened in 0.2 per cent. of pollen-mother-cells. (5) On pollinating tetraploids by diploids, the proportions of 3n, (3n-1), and (3n+1) progeny agreed with the hypothesis that there was approximately 25 per cent. of the 23 + 25 distribution of chromosomes in the reduction division of the megaspore-mother-cells. (6) When tetraploid Daturas are pollinated by diploids, there are produced also many diploid progeny, whose mode of origin is as yet unknown.

Sexual Dimorphism in Mucorales. I. Intraspecific Reactions

Introduction In a previous paper (7) experimental evidence for a strict sexual dimorphism in Cwnninghamella has been given in some detail. The literature bearing on the question of sexuality in the Mucors is there cited, especially as it offers evidence in regard to sexual dimorphism in this group of fungi. In a still earlier publication (5) detailed tests are given for a single species of A bsidia, as well as a provisional summary of tests with other forms. The methods employed in collecting the races studied, making the tests, and tabulating the reactions have already been described (6). The purpose of the present paper is to give in a series of tables the results of testing races within species other than those already recorded. In a second paper in this issue are given the results of testing together races belonging to different species. Most of the tests recorded were made during the years i9i9I923. Unless otherwise noted, the cultures were run at laboratory temperature on our standard nutrient, no. 230, consisting of 2 per cent each of agar, dry malt, and dextrose, with o.i per cent peptone. Other nutrients used were no. 360, consisting of no. 230 Plus 0.5 per cent dried horse dung decoction; no. 362, consisting of agar with addition of 2 per cent whey powder plus i per cent dextrose; no. 388, consisting of agar with 6 per cent malt and i per cent dextrose; no. 39I, consisting of 3 per cent dextrose with i per cent dried horse dung decoction. In the tables the letters A to D are used to indicate the different strengths of sexual activity measured by the relative number of zygospores produced in the given contrasts. Each race has been given a final numerical grade, made up of the average of its reactions with the testers of opposite sex (grade A having the numerical rank 4,

Differentiation of Sex in Thallus Gametophyte and Sporophyte

IN a recent article (5) the writer has given a somewhat detailed account of zygospore germinations in certain species of the Mucorineae. The purpose of the present paper is to point out the bearing which the investigations already made in this group may have upon the questions of sexuality in other forms. Some of the problems for research which the facts observed in the mucors would suggest will be indicated, and it is hoped that in forms in which an alternation of generations occurs the distinction between differentiation of sex in the gametophyte and that in the sporophyte will be more clearly drawn than has been done previously. The various grades of differentiation in the gametes themselves or in the gametophyte and sporophyte will not be discussed. The subject for consideration rather will be the sexual condition in the plant as a whole. According to the sexual character of their thalli, the species of the Mucorineae have been divided (2-6) into two main groups, homothallic and heterothallic-designations which correspond in the main to the terms hermaphroditic and dioecious respectively. In a homothallic species the thalli are all sexually equivalent, while in a heterothallic species the thalli are of two different kinds, which have been provisionally designated by the symbols (+) and (-). The sexual character of the (?) and (-) mycelia remains constant when

Imperfect Sexual Reactions in Homothallic and Heterothallic Mucors

Imperfect sexual reactions were tested between homothallic species (including both homogamic and heterogamic forms) and (+) and (-) races of heterothallic species. Among the heterogamic hermaphrodites there are two sexual groups: (1) those with a (-) sexual tendency (A. spinosa, Dicranophora, Z. moelleri, Z. vuillemini, Zygorhynchus sp.); these show strong reactions with (+) races and weak or no reactions with (-) races; and (2) those with a (+) tendency (Z. heterogamus). These show strong reactions with (-) races and weak or no reactions with (+) races. So far as investigated, all the races of a given species have the same sexual tendency. The terminal and lateral zygophoric hyphae of the hermaphrodites investigated are bisexual. The terminal hyphae take part more actively in imperfect sexual reactions than do the lateral branches. In the group of hermaphrodites with a (-) tendency, the large gametangium is shown to be (+) from its reactions with (-) races and the small gametangium is shown to be (-) from the reaction with (+) races. In the group with a (+) tendency, represented by Z. heterogamus, however, the large gametangium is shown to be (-) in reaction and the small gametangium to be (+). Representative hermaphrodites of these groups when grown together have given imperfect reactions. A small gametangium of the one group reacts with a small gametangium from the representative of the other group, or less frequently two large gametangia, one from each group, show a mutual reaction.

Pollen Tube Growth and Control of Gametophytic Selection in Cocklebur, a 25-Chromosome Datura

1. Pollen tube distributions were plotted from 12-, 16-, and 18-hour tests, using the pollen of the primary (2n + 1) Cocklebur germinated and grown on the pistils of 2n plants. These tests were compared with similar tests of pollen tube growth of normal plants in line 1a. 2. Further evidence is given from the results of ordinary male back-crosses of Wedge to four lines, indicating that the latter is a secondary (2n + 1) type related to Cocklebur. Pollen tube distributions obtained from the pollen of Wedge are also plotted. 3. The pollen tube distribution curves indicate that Cocklebur may be transmitted through the pollen under conditions in which the processes of gametophytic selection are controlled experimentally. Likewise, the distribution curves indicate that Wedge may not be transmitted through the pollen in line 1A. 4. The correctness of the interpretations gained from pollen tube distribution curves was tested genetically in the case of Cocklebur, by combining three other experimental methods: the effects of restricted pollinations; the effects of excision of styles; and the separation of the seeds in the lower half of seed capsules from those in the upper half. Results from all experimental methods confirmed the interpretations gained from a study of pollen tube distribution curves. 5. The various methods which have been used by investigators at different times in a study of the effects of gametophytic selection are briefly discussed and compared. 6. The pollen tube distribution curves obtained from suitable tests enable us to recognize processes of gametophytic selection, and have the further advantage of enabling us to distinguish between at least five different conditions, all of which may lead to the complete or partial elimination of some of the classes of male gametophytes, resulting in modified ratios in the progeny. 7. The processes of gametophytic selection involved in the pollen transmission of Cocklebur may be controlled through a wide range. A threefold increase may be obtained by restricted pollinations, and a further increase, up to 65 per cent Cocklebur plants, may be obtained in a progeny by selecting the seeds to be planted from the lower parts of seed capsules, while complete non-transmission of Cocklebur may be obtained by properly timed excisions of styles.

Trisomic Inheritance in the Poinsettia Mutant of Datura

(1) The (2n + 1) mutant Poinsettia in Datura Stramonium is briefly described. (2) The frequency of its new occurrence in offspring of 2n parents is about once in two to three thousand individuals. (3) The extra chromosome responsible for the peculiarities of the Poinsettia mutant, (a) is not transmitted through the pollen or to only a slight extent; (b) is transmitted through only about 30 per cent. of the egg cells; (c) is transmitted to a slightly larger proportion of the offspring when the Poinsettia parent is pollinated from a normal or from another Poinsettia than when it is selfed. (4) It is, therefore, concluded: (a) that the condition in the Poinsettia is similar to that previously found for the Globe mutant in that gametes with the extra chromosome are less viable than those with the normal (n) number, and (b) that crossing the mutant with a normal or with another Poinsettia in comparison with selfing probably gives increased vigor and therefore increased survival value to the (2n + 1) zygotes which result. (5) The theoretical ratios are given for trisomic inheritance based upon non-transmission of the extra chromosome through the pollen and upon the assumption of random assortment of chromosomes within the trisome. (6) Both the phenotypic and genetic ratios for the inheritance of purple pigmentation in the offspring of Poinsettia parents agree closely with the theoretical ratios. (7) It is therefore concluded: (a) that Poinsettia has its extra chromosome in the set which carries the genes for purple and white flower color, and (b) that the three chromosomes in this set assort at random.

1921, Types of mutations and their possible significance in evolution

Den Beschlul~ der Arbeit bildet eine systematische Ubersicht und ein Stammbaum. Zu erw~hnen ist noch, dab die festgestellten Entwicklungen stets auch als Anpassungen gedeutet werden. Bei den 8epioidca und Teuthoidea bestehen diese wesentlich in einer ErhOhung der Beweglichkeit auf Kosten der Panzerung. Bei jenen spielt aufierdem auch die Sicherung einer horizontalen Schwimmstellung eine wichtige Rolle. Die Ftille yon Stoff, die das Buch auf wenig mehr als 300 Seiten enth~it, ist eine ganz aufierordentliche. Besonders die Erkliirungen zu den 100 Textfiguren bringen in ktirzester Form eine Unmenge von Tatsachen, das Ergebnis langer, umst~ndlicher Untersuehungen. Auch die Bewiiltigung der reichen und so sehr zerstreuten Literatur stellt eine bedeutende Leistung dar. Sehliei~lich sei noch auf die grofie Klarheit und Sauberkeit der vom Verf. selbst gezeichneten Abbildungen hingewiesen. Alles in allem ein Werk, das man mit dem Wunsch aus der Hand legt, wir mSchten recht bald ftir mSglichst viele Tiergruppen ~thnliche Zusammenfassungen erhalten. J. Pia.

A chemical method of distinguishing genetic types of yellow cones in Rudbeckia

Sei~ I. In t roduct ion . . . . . . . . . . . . . . . . . . . . . . 211 I L Origin of Yellow Coned Races . . . . . . . . . . . . . . . . 212 I I I . Chemical Tests . . . . . . . . . . . . . . . . . . . . . 213 IV. Inheritance of Black Yellows . . . . . . . . . . . . . . . . 215 V. Inheri tance of Red Yellows . . . . . . . . . . . . . . . . . 216 VL Crosses between Black Yellows and Red Yellows . . . . . . . . . 216 V I I . Discussion . . . . . . . . . . . . . . . . . . . . . . 220 V I I I . Summary . . . . . • . . . . . . . . . . . . . . . . . 221