A. Fahn

Secretory Hairs of Inula viscosa (L.) Ait.-Development, Ultrastructure, and Secretion

The leaves and young stems of Inula viscosa (L.) Ait. bear sessile and stalked secretory hairs which secrete throughout the life span of the leaf from its very early stage of development to maturity. Both types of hair possess a secretory head consisting of three types of cells: one pair of summit cells, one pair of cells below the summit cells, and three pairs of photosynthesizing cells. All head cells secrete lipids, polysaccharides, and protein. In the head cells smooth and rough endoplasmic reticulum, plastids, mitochondria, and Golgi bodies seem to be involved in secretion. The various cell pairs of the head differ in their sequence of ultrastructural changes throughout the period of secretory activity, in type of plastid and its involvement in the secretory process, and in the manner the substances secrete to the outside. At various stages of the secretory activity different cell constituents were present in abundance.

Functions and location of secretory tissues in plants and their possible evolutionary trends

On the basis of the variability and location of the secretory tissues in the plant body, the following are suggested: (1) In relation to their surrounding environment, the secretory tissues fulfill two very important ecological functions--protection against herbivores and pathogens and attraction of pollinators. (2) The protective function preceded the function of attraction. (3) The protective secretory tissues are suggested to have expanded during the course of evolution from the leaf mesophyll outside, to the epidermis and its trichomes, and inside the plant body, to the primary and secondary phloem, and, in a few cases, also to the secondary xylem.

SEED ANATOMY OF PANCRATIUM SPECIES FROM THREE DIFFERENT HABITATS

The anatomy of seeds from three species of Pancratium occupying different habitats was examined. Pancratium maritimum grows on the spray belt of the Mediterranean shore, P. sickenbergii in sandy soil in the steppe regions, and P. parviflorum in the Mediterranean batha. Seed development was found to be similar in all three species. All the walls of the seed coat cells derived from the outer integument are encrusted with a highly resistant brown-black material which apparently consists of phenolic quinones. Two or three compressed outer layers of cells of the testa of P. maritimum and P. sickenbergii form a dark protective layer. The rest of the testa in these two species is composed of large, dead, air-filled cells with large intercellular spaces between them In contrast, the seed coat of P. parviflorum consists of smaller cells with small intercellular spaces; the seed possesses an elaiosome containing two types of lipid. The differences in characteristics of the testa among the three species are of adaptive value in the different habitats in which the plants grow.

Ultrastructural observations on the foliar secretory cavities of Porophyllum lanceolatum DC. (Asteraceae)

Summary The ultrastructure of foliar secretory cavities of Porophyllum lanceolatum DC. was studied at three developmental phases, and shows to have the basic characteristics of terpene-secreting glands. The ability to secrete is already present in young, differentiating cavities. In the epithelial cells, dark osmiophilic material occurs in plastids, mitochondria, the nuclear envelope, the endoplasmic reticulum (ER) and dictyosomes, indicating the participation, in some way, of such structures in the secretory process. The ER is seen to be associated with plastids (periplastidal ER), mitochondria and the nuclear envelope, seeming to play a role in transporting the secretory material from these organelles to the plasmalemma. The granulocrine mechanism, involving portions of ER, and independently, vesicles derived from dictyosomes, is considered to be the main process for the elimination of secretory material from the protoplast. Multivesicular, multilamellar and mixed bodies were also observed, as well as microbodies (associated with ER in some cases), in the epithelial cells. In the cells of the gland sheath the walls are thicker than those of the epithelial cells; starch is often present in their plastids

The development and ultrastructure of gum ducts inCitrus plants formed as a result of brown-rot gummosis

SummaryYoung stems ofCitrus plants were infected with the fungusPhytophthora citrophthora. The effect of the infection on gum duct development was studied. The following sequence of structural changes was observed in the cambial zone: 1. The middle lamellae between layers of xylem mother cells dissolve forming duct cavities. 2. The cells around the duct cavities differentiate into epithelial cells rich in cytoplasm. 3. The amount of Golgi bodies and associated vesicles increases. The vesicles and small vacuoles, some of which seem to originate from the fusion of Golgi vesicles, contain fibrillar material that stains for polysaccharides. Vesicles and vacuoles appear to fuse with the plasmalemma. Material staining positively for polysaccharides accumulates between the plasmalemma and cell wall, and penetrates the latter. 4. The protoplast shrinks and the space below the cell wall, which contains polysaccharides, increases in volume. 5. After a period of 10 days or more the gum ducts become embedded in the xylem, and the activity of the epithelial cells ceases. The cell walls of many of them break, and the gum still present in the cells is released.

SEASONAL CAMBIAL ACTIVITY AND PHYTOGEOGRAPHIC ORIGIN OF WOODY PLANTS: A HYPOTHESIS

An attempt was made to examine the hypothesis that the annual course of cambial activity is a permanent feature of each woody plant, related to its phytogeographic origin. Existing data on cambial activity in woody plants growing in Israel have been presented in a comprehensive diagram which shows a correlation between the course of activity and the phytogeographic origin of the various plants. Some attempts to prevent the occurrence of a period of cambial dormancy in plants which normally have such a period were unsuccessful.

Cell hypertrophy in stems ofPinus halepensis infested byMatsucoccus josephi

SummaryStructural and ultrastructural changes occurring in the living cells of young plants ofPinus halepensis Mill. artificially infected withMatsucoccus josephi Bodenheimer et Harpaz, were studied. The study revealed that, opposite the places of attachment of the insects to the stem, groups of enlarged cells occurred in the cortex and often also in the phloem and cambial zones. In the enlarged cortical parenchyma cells there was a pronounced increase in the volume of the cytoplasm. The nuclei were large and lobed. The ER appeared in two forms, in very long cisternae arranged in parallel, and in short variously oriented tubules. The plastids were without grana, contained a tubular network and many plastoglobuli. Mitochondria and dictyosomes were relatively numerous. The function of the hypertrophic cells is discussed.