180 Dr. H. Charlton Bastian on Diatoms and the 
(5) The diatoms have been produced zn situ by a trans- 
formation of the fission-products of the alga. 
The first of these possibilities it will be convenient to speak 
of as the Infection Hypothesis and the second as the Trans- 
formation Hypothesis. 
(a) Infection Hypothesis.—The difficulty in accounting for 
the facts seems to me to be extreme in accordance with this 
supposition, especially if we bear in mind what is authorita- 
tively known concerning diatoms. ‘The important points are 
these :— 
1. No motile spores are known, and previous to 1896 there 
was no certain knowledge concerning the existence of spores 
of any kind in diatoms. ‘The important discovery by George 
Murray of undoubted spores or germs, originating by a pro- 
cess of rejuvenescence, in species belonging to three marine 
genera * constitutes all that is certainly known at present on 
this subject. 
2. It is commonly stated by writers that individual diatoms 
do not increase in size}, increase in bulk of diatoms being 
only brought about asa result of ‘ conjugation,” which is 
admitted to be a comparatively rare process. 
3. Previous to the above-mentioned discovery by George 
Murray diatoms were said to be formed only (a) by a process 
ot ‘ conjugation ” or rejuvenescence, or (0) by fission, which 
is the common process, and one that involves a very slight 
diminution in size of the products f. 
Such facts concerning diatoms in general must be borne in 
mind in conjunction with these others more specially bearing 
upon the question now under consideration. 
4, The substomatal spaces which either are or have been 
tenanted by Chlorochytrium probably constitute much less 
than 10 per cent. of those existing on most leaves of the 
duckweed, yet no diatoms are ever to be seen in the other 
90 per cent. of the substomatal spaces, 
5. The purposeless to-and-fro movements of some diatoms 
when free in a fluid, and their absence of movement when 
lying on the surface of a leaf, seem quite incompatible with 
the notion of their selective penetration through certain 
special stomata only. 
6. A point of still greater importance is the fact that 
* Proc, Roy. Soc. Edinb. 1896-97, p, 207. 
+ Wolle, ‘ Diatomaceze of North America,’ 1890, p. 11; Smith’s 
‘ British Diatomacee,” vol. i. 1853, p. xxiv, and 1856, vol. ii. p. vii; and 
Pritchard, 4th ed. 1861, pp. 58, 61-63. 
t Wolle, doc. cat. p. 11, 
