IX 



MA RA TTIA CE^- ISOE TA CE^ 



289 



during its rapid elongation separates in places, and forms a 

 system of large intercellular spaces. There are two rows of 

 very large ones, forming two broad air-chambers extending the 

 whole length of the leaf, but which are interrupted at intervals 



Fig. 153. — A, Median section of a young sporophyte with the second leaf L'- already formed ; r", 

 second root ; st, stem-apex, X 150 ; B, cross-section near the base of the cotyledon, showing the 

 intercellular spaces i and the second leaf L2 surrounded by the sheath v at the base of the coty- 

 ledon ; /, the ligule of the cotyledon, X 300. 



by imperfect partitions composed of single layers of cells. In 

 the root there are similar lacunae, but they are smaller and 

 less regularly arranged. 



u 



