204 MISCELLANEOUS EXAMPLES 



of their selective penetration through certain special stomata 

 only. 



6. A point of still greater importance is the fact that Diatoms 

 are never to be seen in the spaces in which the Chlorochytrium is 

 in one of its early stages of development ; they are to be found 

 only in association with its later stages, where some of the iinal 

 segmentations have been taking place, and often where the patches 

 are so old that the walls of the spaces containing them are stained 

 a rust colour. 



7. None of the Diatoms found either within the spaces or within 

 their ramifications between surrounding cells have ever been seen 

 to move. 



8. Moreover, where the Diatoms exist they are often intimately 

 intermixed with the algoid cells ; they are also to be seen in the 

 ultimate ramification of spaces, even when these are still full ; and 

 small specimens are likewise to be found between surrounding sub- 

 epidermal cells contiguous to the invaded space. Such facts are 

 incompatible with an entry of Diatoms from without, if we bear in 

 mind what has been said under the last two heads. 



9. Again, where the Diatoms exist they not only vary much in 

 size and shape in different spaces, but even within different regions 

 of the same space. 



Taken as a whole, these various facts seem to me absolutely to 

 negative the Infection Hypothesis as a means of accounting for the 

 association of Diatoms with the fission products of Chlorochytrium 

 in the sub-epidermal spaces. 



(b) Transformation Hypothesis. The facts which are so incom- 

 patible with the foregoing hypothesis will be found to offer no 

 difficulties to, or to be capable of receiving a ready explanation in 

 accordance with, the transformation hypothesis. This hypothesis 

 is also strengthened by other facts not previously referred to. 



1. The absence of the Diatoms from the ninety per cent, of the 

 sub-stomatal spaces which are not infected by the Alga is explained. 



2. The absence of movements on the part of the Diatoms in 

 question affords no difficulty. 



3. The absence of the Diatoms from the Chlorochytrium spaces 

 during the early stages of the development of the Alga affords no 

 difficulty and is explained. 



4. The variation in the size of the Diatoms is explained, in the 

 main, by the varying size of the fission products of the Alga. The 



