300 



THALLOPHYTES. 



considered. The segment /// becomes the first internode of the leaf, II becomes a node 

 from which are developed the lateral leaflets nb'inC and D. The cell / divides into two 



Fig. 200.— Development of the antheridia oi Nitellajlexilis. In B, C, and D the protoplasm has been 

 contracted by glycerine. 



(C, I), the lower of which remains short, while the upper grows into a flask-shaped cell 

 (Fig. 200, D,f, and Fig. 201,/). 



The globular mother-cell of the antheridium (Fig. 200, ^, a) first of all divides into 

 two hemispheres by a vertical wall passing through the axis of the leaf ; each of these 

 is divided into two segments by a vertical wall at right angles to the first ; in each of the 



four quadrants a third division takes place hori- 

 zontally and at right angles to the two last walls ; 

 and the antheridium now consists of four lower 

 and four upper octants of a sphere. Contrac- 

 tion by glycerine clearly shows that each of 

 these divisions of the protoplasmic body is com- 

 pletely effected before the appearance of the 

 cellulose-wall (Fig. 200, B) ; the second division 

 even takes place before the wall has arisen 

 between the two first-formed halves; and the 

 four quadrants may be made to contract without 

 any wall being visible between them. In Fig. 

 200, 5, the third division has also taken place, 

 the second vertical wall is already formed, and 

 the two quadrants there visible are already 

 divided ; but no horizontal wall has yet appeared. 

 In Fig. 200, A, a, are shown the eight octants 

 in perspective together with their nuclei. Each 

 octant now breaks up first of all into an outer 

 and an inner cell (Fig. 200, C) ; the latter is 

 again divided in all the eight octants (D), so 

 that each octant now consists of an inner, 

 a middle, and an outer cell {D, i, m, e). Up 

 to this time the globe remains solid, and all 

 the cells lie close to one another ; but now 

 commences an unequal growth, and with this 

 the formation of intercellular spaces (Fig. 201). The eight outer cells {e) are the young 

 shields, the side-walls of which show even at an earlier period the radial infolding 

 already mentioned; they grow more strongly in a tangential direction than the inner 



Fig. 201.— Antheridium of Nittllaflexilis in a further 

 stage of development (x about 500). 



