286 



MOSSES AND FERNS 



CHAP. 



embryo. It projects but little, and the cells are not noticeably 

 larger than those of the cotyledon and root. 



As the cotyledon lengthens it becomes somewhat flattened, 

 and in the later stages its increase in length is due entirely to 

 basal growth. Even in very young embryos a distinct 

 epidermis is evident in the leaf, and about the time that the 

 ligule is formed the first trace of the vascular tissue appears. 



1. ■. 



D 



B. 



Fig. 150. — Development of the embryo in /. echinosfiora var. Braunii (Dur.). A, Median longi- 

 tudinal section of a young embryo ; B, four horizontal sections of a younger one ; C, two vertical 

 transverse sections of an older embryo ; /, the ligula, X 300. 



This consists of a bundle of narrow procambium cells, which 

 lie so near the centre of the embryo that it is impossible to 

 assign it certainly to either root or leaf ; indeed it sometimes 

 seems to belong to one quadrant, sometimes to the other. 

 From it the development of the axial bundles of cotyledon and 

 root proceeds, and by it they are directly united. The section 

 of the plerome cylinder of the leaf is somewhat elliptical, and 



