252 



BOTANY 



applied. As already stated, the attractive substance thrown out has 

 been shown to be malic acid. 



The Embryo 



In the common Ferns the first division of the embryo does not 

 occur for a week or more after fertilization. The globular embryo 

 (Fig. 216) then divides by a nearly vertical " basal " wall into two 

 cells, an epibasal (anterior) and an hypobasal (posterior). Each of 



A. 



FIG. 216. A, B, Osmunda Claytoniana. C, 0. cinnamomea. A, vertical section 

 of an 8-celled embryo (x 260). B, median longitudinal section of an older embryo, 

 showing the primary organs ; stem,.s; leaf, I; root, r; foot,/. C, two transverse 

 sections of an embryo, showing the apical cells of stem and root; the first root-cap 

 cell has not yet been cut off. 



these is next divided by a transverse wall into two usually equal 

 parts, and this establishes the primary organs of the sporophyte. 

 Of the epibasal quadrants, the outer one becomes the cotyledon, or 

 primary leaf ; the inner one, the stem-apex. Of the hypobasal quad- 

 rants, the outer gives rise to the primary root, the other to the foot. 

 Stem and Cotyledon. Following the quadrant-walls are the octant- 

 walls, which are not always exactly median in position, this being 

 especially the case in the root-quadrant, where one octant is usually 

 noticeably smaller than the other. Each octant is a tetrahedron, and 

 the next divisions in all of them are parallel to the lateral faces of 

 the octant-cells. These divisions persist in one of the stem and leaf 

 octants which assume the function of apical cells for these organs. 



