DE VEL OPMENT. 



99 



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

 cells" derived from the two posterior quadrants remains con- 

 nected with the prothallium as an organ for the absorption of 

 nutriment from the latter, and is inappropriately called the foot. 



em. 



Fio. 67. (After Hofmeister.) Development of the embryo. A, section showing the closed 

 neck (n) and the planes of quadrant division of the ouspore 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; rh, rhizome. 



FIG. 68. (From Luerssen, after Kienitz-Gerloff.) Development of the embryo of Pteris 

 serrulata. 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 C 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 (6) 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, I, and s soon take on apical growth as indicated in H and /. 



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.' 1 ' 1 



The several parts now enter upon rapid growth accompanied 

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

 sented in C, Fig. 67. A stage somewhat later than this, with 

 its attachment to the prothallium, is shown in Fig. 69. After 

 this the leaf grows upwards into the air, the root downwards into 

 the earth, and the young fern begins to shift for itself. Event- 



