214 



MONOSTROMA, ULVA, AND NITELLA LESS. 



traced into the crown, and in young specimens its interior is 

 readily seen to be occupied by a large opaque mass (ov). 

 Sections show that this central body is the ovum, a large cell 

 very rich in starch : it is connected with the unicellular stalk 

 by a small cell (nd) from which spring five spirally-arranged 

 cells (sp. c) : these coil round the ovum and their free ends 

 each divided by septa into two small cells project at the 

 distal end of the organ and form the crown, enclosing a 



nil 



FIG. 47. A, vertical section of the ovary of Nitella, showing the 

 stalk (stk), small node (nd) from which spring the five spirally-twisted 

 cells (sp. c), each ending in one of the two-celled sections of the crown 

 (cr). The ovum contains starch grains, and is represented as trans- 

 parent, the spiral cells being seen through it. 



B 1 * surface view, and B 2 , section of a very young ovary : B 3 , later 

 stage in vertical section : B 4 , still later stage, surface view, with the 

 ovum seen through the transparent spiral cells. Letters as in A, except 

 x, small cells formed by division from the base of the ovum. (B 2 -B 4 

 after Sachs. ) 



narrow canal which places the distal end of the ovum in free 

 communication with the surrounding water. 



We saw how the various parts of the fully formed plant 

 nodal, and internodal cells, leaves, and rhizoids were all 

 formed by the modification of similar cells produced in the 

 apical bud. It is interesting to find that the same is true of 

 the diverse parts of the reproductive organs. 



The spermary arises as a single stalked globular cell which 



