212 NITELLA 



repeated fission of the nucleus reminds us of what was 

 found to occur in Opalina (p. 119). 



Then*the growth of Nitella like that of Penicillium (p. 

 1 88), is apical : new cells arise only in the terminal bud, 

 and, after the first formation of nodes, internodes, and 

 leaves, the only change undergone by these parts is an in- 

 crease in size accompanied by a limited differentiation of 

 character. 



A shoot arises by one of the cells in a node sending 

 off a projection distad of a leaf, i.e., in an axil : the process 

 separates from the parent cell and takes on the characters of 

 an apical cell of the main stem, the structure of which is in 

 this way exactly repeated by the shoot. 



The leaves, unlike the branches, are strictly limited in 

 growth. At a very early period the apical cell of a leaf 

 becomes pointed and thick-walled (Fig. 46, E), and after this 

 no increase in the number of cells takes place. 



The rhizoids also arise exclusively from nodal cells : they 

 consist of long filaments (Fig. 46, c), not unlike Mucor- 

 hyphae, but occasionally divided by oblique septa into linear 

 aggregates of cells, and increase in length by apical growth. 



The structure of the gonads is peculiar and somewhat 

 complicated. 



As we have seen, the spermary (Fig. 46, G, spy) is a 

 globular, orange-coloured body attached to a leaf by a short 

 stalk. Its wall is formed of eight pieces or shields, which 

 fit against one another by toothed edges, so that the entire 

 spermary may be compared to an orange in which an equa- 

 torial incision and two meridional incisions at right angles 



O O 



to one another have been made through the rind dividing 

 it into eight triangular pieces. Strictly speaking, however, 

 only the four distal shields are triangular : the four proximal 



