OF HETEROGENESIS 201 



X 250), or of very different sizes. Other spaces may be seen still 

 full and distended with Chlorochytrium, the constituent cells of 

 which exhibit very different degrees of segmentation, as in Fig. 28, 

 A. Some have become resolved into the very minute zoospores as 

 in B (x 375), while others, have remained as fission products 

 varying much in size. 



Thus the Chlorochytrium cells are found to undergo processes 

 of division to a variable extent so as to yield fission products of 

 very different sizes ; and, presumably under the influence of some 

 unfavourable conditions in their environment, some of the products, 

 at each of these stages, may undergo no further changes of a 

 normal kind. 



This brings me to one of the important points now to be made 

 known — which is, that in the later stages of the life of Ch. Knyamim 

 the fission products, within the intercellular spaces of the leaf, are 

 often found to be more or less intermixed with Diatoms, varying 

 much both in size and shape. 



This association is met with sometimes in spaces none of the 

 contents of which have escaped, and then the contrast is great 

 between the beautiful emerald-green of the algoid cells and the 

 brownish-yellow colour of the Diatoms mixed therewith. At other 

 times partially empty spaces are seen containing the fission 

 products of the Alga alone (Fig. 28, C), Diatoms alone as in D 

 ( X 250), or a mixture of the two kinds of units. 



More rarely, spaces are found densely packed with brownish- 

 yellow Diatoms only, in different stages of growth and develop- 

 ment, except perhaps for the association of one or two minute 

 algoid corpuscles. 



In regard to the Diatoms themselves, they are sometimes very 

 small and rudimentary, or they are much larger ; and these larger 

 sizes are either fairly broad and ovoid like Naviculae, or else narrow 

 and elongated, like Nitzschiae. 



In almost all cases, however, the Diatoms have the appearance 

 of being immature ; they have ill-developed siliceous envelopes, 

 and are all quite full of brownish-yellow endochrome. There are 

 also, at times, indications that growth and multipUcation of these 

 immature forms is, or has been, taking place — looking to the way in 

 which they are occasionally ranged side by side in short rows in 

 some of the half-empty spaces. 



The sub-stomatal spaces which have been tenanted by the Chloro- 



