362 



BOTANY 



is the transformed stem-apex. The ovule, or macrosporangiuin, 



may also be of axial origin 

 instead of an outgrowth of 

 the carpel (Naias, Pepe- 

 romia, etc.). 



The rnicrosporangium cor- 

 responds in its development 

 with that of the higher Pteri- 

 dophytes and Gymnosperms. 

 With few exceptions, e.g. 

 Naias, Lilaea (Fig. 317), 

 where the sporogenous tissue 

 arises from the plerome, this 

 tissue is derived from a layer 



of hypodermal cells by the 

 FIG. 316. Capsella oursa-pastons. Develop- - i P / 



ment of the flower (x about 75). A, two formation of a series of peri- 

 very young flowers; in II the sepals, s, have clinal walls which form a 

 just appeared. B-D, older stages, optical tapetal layer between the 

 sections; r, receptacle; s, sepals ; p. petals ; ,. -, ,-, 



6, stamen; ?, carpels. sporogenous tissue and the 



epidermis. The pollen mo- 

 ther-cells usually separate before the first nuclear division occurs, 

 and often have very thick gelatinous wall". The first nuclear divi- 



A 



D 



FIG. 317. A, Naias ftexilis. Section of young staminate flower, highly magnified; 

 the anther is terminal and closely resembles the young ovule, both in position and 

 in the possession of an integument, in; the sporogenous cells have the nuclei 

 indicated. B-D, Lilsea subulata. B, cross-section of young anther, showing the 

 four lobes or pollen-sacs ( X 200) . C, part of an older pollen-sac, showing the large 

 sporogenous cells and tapetum, t. D, cells from the wall of a ripe anther, show- 

 ing the "fibrils" (x 400). 



