140 



THE BIOLOGY OF A PLANT. 



lower anterior quadrant as it undergoes further division grows 

 out into t\iQ Jirst root y the upper anterior quadrant in like man- 

 ner gives rise to the rhizome and the first leaf. The mass of 

 cells derived from the two posterior quadrants remains connected 

 with the prothallium as an organ for the absorption of nutri- 

 ment from the latter, and is inappropriately called tliefoot. 



em. 



I 



^ J 

 rh. 



FIG. 79. FIG. 80. 



FIG. 79. (After Hofmeister.) Development of the embryo. A, section showing the 

 closed neck (ri) and the planes of quadrant division of the oospore or embryo (em). 

 The fore end of the prothallium is to the right. B and C, stages of the embryo 

 later than A, showing the beginnings of apical growth ; /, foot ; ?, leaf ; r, root ; 

 rft, rhizome. 



FIG. 80. (From Luerssen, after Kienitz-Gerloff.) Development of the embryo of 

 Pteris scrrulata. The figures are optical sections taken vertically in the antero- 

 posterior axis of the prothallium, passing through the long axis of the neck of 

 the archegonium ; except G and D, which are taken at right angles to the others. 

 A< a, and p are the anterior and posterior segments of the oospore after this has 

 divided into hemispheres. The former (a) forms the stem, the latter (p) the root. 

 F shows in a late stage the division of the quadrants, r going to form the root, s 

 the stem or rhizome, I the leaf, and / the foot ; r, Z, and s soon take on apical 

 growth as indicated in H and I. 



In Pteris serrulata the development is slightly different. The lower 

 anterior cell becomes the first leaf ; the upper anterior becomes the first 

 portion of the rhizome, the lower posterior becomes the primary root, and 

 the upper posterior remains as the " foot." 



The several parts now enter upon rapid growth accompanied 

 by continued cell-multiplication, until a stage is reached repre- 



