I W Bailey

The Structure of the Wood in the Pineae

1. Wood-parenchyma occurs on the outer surface of the summer wood of Picea. It is sporadic in its occurrence, and while usually appearing infrequently, may be strongly developed. 2. Wood-parenchyma may be very sparsely developed in Larix and Pseudotsuga. 3. Septate tracheids occur associated with the wood-parenchyma in these three genera, and show clearly the steps by which wood-parenchyma has been developed from tracheids. 4. Septate tracheids occur in Pinus, and wood-parenchyma very rarely. 5. Spiral thickenings of the tracheids occur in both the spring and summer wood in Picea and Pseudotsuga, and occur in the summer wood of Larix. These thickenings occur also in Pinus. 6. Spiral thickenings of the marginal and interspersed tracheids of the rays occur in Pinus, Picea, and Larix, as well as in Pseudotsuga. 7. The anatomical characters of the wood are so variable and so similar in Picea, Larix, and Pseudotsuga, that it is difficult to distinguish the extant or fossil woods of the genera. 8. Pinus appears to be quite distinct from the other living Pineae. Yet in the nut and foxtail pines, we see a condition resembling the condition in Picea, Larix, and Pseudotsuga. These pines have small rounded pits in the ray cells, have tangential pits like Picea, have thick-walled epithelium in the canals, and spiral thickenings in the ray tracheids. 9. Picea approaches nearer to the condition in Pinus by having more numerous thin-walled epithelial cells and tyloses, and less well-developed wood-parenchyma; yet Larix and Pseudotsuga also have thin-walled epithelial cells occasionally, and may have the wood-parenchyma poorly developed.

Anatomical Characters in the Evolution of Pinus

Pinitus is the oldest genms of the conifers and the most important and interesting, whether considered from the botanical, economic or aboricultural standpoint. Occurring as it does in many species throughout the whole northern hemisphere, from it are derived many of the most valuable timbers and extractable products of cornnerce. In accordance with the general impression, that flourishing genera are modern, since they show an obvious adaptation to existing conditions of environment, it has been assumed that Pinus is of comparativelyrecent origin and marks the last word as it were in coniferous development. Recent investigations however of the occurrence of Pinus in the American Cretaceous, show that in the lower levels of that epoch, species of pines were apparently much more numerous than they are at the present time. It is accordingly apparent that so ancient a genus as Pinus and one so richly endowed with aan abundant moclerii progeny supplies a particularly favorable subject for evolutionary investigation. It has been the practice in the past to arrange plants systematically on the basis of external characters alone, chiefly on the superficial features of their floral organs and leaves. In the case of so ancient a genus as that under consideration, this procedure has peculiar difficulties connected with it, since in the tremendous period of time duriiig which it has beeii in existence, its external characters have undergone rnany puzzling changes. The internal structure of the genus however has shown

Structure, Development, and Distribution of So-Called Rims or Bars of Sanio

1. Bandlike thickenings of the middle lamella and scalariform primary pit areas are characteristic of tracheids which have scalariform bordered pits. They are widely distributed among the Pteridophyta, Gymnospermae, and Angiospermae. 2. The middle lamella frequently retains its typical scalariform structure after the secondary wall has lost it. 3. In the Gymnospermae, as well as in the Pteridophyta and Angiospermae, there appear to be transitions between primary membranes of this type and others in which the scalariform structure is profoundly modified. 4. The comparative anatomy and ecology of the Pteridophyta, Gymnospermae, and Angiospermae afford considerable evidence which suggests that the types of unconformity and peculiar bandlike thickenings of the middle lamella (so-called bars or rims of Sanio) which occur in certain Pteridophyta and Angiospermae, as well as in many Gymnospermae, are concomitants of processes of modification or reduction in tracheary pitting. 5. The structure of the walls of the cambium and the development of the pitting in the elements of the xylem and phloem in Pteridophyta, Gymnospermae, and Angiospermae deserve more careful consideration in discussions concerning the phylogenetic significance of the so-called rims or bars of Sanio, than they have received heretofore.

Depressed Segments of Oak Stems

From observations of transverse sections of twigs from Quercus alba, Q. bicolor, and Q. macrocarpa I find that there is evidence of retardation in growth of the tissues in the immediate vicinity of the wide rays, especially noticeable in the marked dipping in of the annual rings where they cross the large rays. However, aside from a few extreme cases, this checking influence of the wide foliar rays does not explain the 5 conspicuous depressions o characteristic of the wood of Quercus.

Microtechnique for Woody Structures

In the preparation of thin sections (5 /x or less) of hard tissues the celloidin method has been largely used with excellent results. The method as originally described by PLOWMAN7 has been modified during the last few years at the laboratories of plant morphology of Harvard University, to meet the demands of work with special classes of hard tissues. In reply to numerous inquiries as to the best method of preparing thin sections of woody tissues (trees and shrubs), and as to the advisability of using the celloidin technique, the following methods of treatment used in preparing slides for photomicrography, the study of wood structure, and instruction in wood technology are described.