440 PHA NER OGAMS. 



short naked peduncle, and on this are seated the numerous staminal or carpellary 

 leaves (Fig. 315). The axis terminates with a naked apex which undergoes no 

 further development (Fig. 315 D). The stamens are, indeed, but small in comparison 

 to the foliage-leaves of the same plant, but are, nevertheless, the largest which 

 occur anywhere among Phanerogams. In Macrozamia, as in Cycas, they are from 

 6 to 8 cm. long, and as much as 3 cm. broad; they spring, with rather a narrow 

 base, from the floral axis, and expand into a kind of lamina, terminating in an 

 apiculus (Macrozamia) or in two curved points (Ceratozamia), or the lower part of 

 the stamen is thinner and stalk-like and bears a peltate expansion (Zamia). They 

 are also distinguished from the stamens of most other flowering plants by their 

 persistence, becoming lignified and often very hard. The numerous pollen-sacs on 

 the under side of the stamens are usually collected into small groups numbering 

 from two to five, like the sori of Ferns, these again forming larger groups on 

 the right and left side of the leaf. The pollen-sacs are globular or ellipsoidal, 

 usually about i mm. in size, and are attached with a narrow base to the under 

 side of the stamen ; Karsten states that in Zamia spiralis they are even stalked. 

 They dehisce longitudinally, and are in all respects much more like the sporangia 

 of Ferns than the pollen-sacs of other Phanerogams, from which they also differ 

 in the firmness and hardness of their wall. The mode of development of the 

 pollen-sacs and pollen-grains of Cycadeae was till lately unknown ; it has only 

 quite recently been observed by Juranyi in Ca'atoza?nia longifolia. The pollen- 

 sacs are formed on the under side of the stamens in the form of small papfllse, 

 probably consisting from the first of several cells over which the epidermis of 

 the surface of the leaf is continuous. The inner tissue is next diff"erentiated 

 (as in the sporangia of Lycopodiaceae, Equisetaceae, and Ophioglossacese) into an 

 outer layer of smaller cells enclosing a larger-celled tissue; since the cells of the 

 latter continue to grow and divide in all directions, the mother-cells of the pollen 

 are finally isolated, but densely crowded together, as in Dicotyledons. The mode 

 of division of the mother-cells is nevertheless more like that of Monocotyledons in 

 this respect, that they first of all split up successively into two daughter-cells, each 

 of which again undergoes bipartition. The first division-wall is formed, as in Dico- 

 tyledons, by the slow growth of an annular ridge of cellulose, formed in the depres- 

 sion produced by the previous constriction of the protoplasm of the mother-cell; 

 but in each of the two daughter-cells the second partition appears to be formed 

 simultaneously, as in Monocotyledons. The four young pollen-cells are now freed 

 by the rapid absorption of the cell-wall which surrounds and separates them. The 

 pollen-grains, when free from their mother-cells, are unicellular and spherical ; but, 

 during their further growth, the contents, enclosed by an extine and intine, divide 

 into two cells, a smaller and a larger one, each possessing a nucleus. The smaller 

 of these two cells, lying on one side against the intine of the pollen-grain, becomes 

 arched on the opposite side, and projects in the form of a papilla into the larger 

 one. This smaller cell now again undergoes a transverse division parallel to the 

 first, and this is sometimes followed by a second; a two- or three-celled body is 

 thus formed, attached on one side to the intine, and projecting into the cavity 

 of the larger' cell, as in Abietineae, from which, however, Ceratozamia differs in 

 the fact that, as in Cupressineae, the large cell, formed by the first division of the 



