DIATOMACEyE. 87 



The true position of the Schtzomycetes is by no means 

 definitely settled. Bennett says, " They are only fungi in the 

 very limited sense of their being ' thallophytes which contain 

 no chlorophyll,' and indeed it has been seen that certain 

 Bacteria do contain chlorophyll. Looking at their morpho- 

 logical characters, as far as these are at present known, it 

 cannot be doubted that the nearest allies of the Arthro- 

 sporous Bacteria are those Protophyta, Nostocaceae, Oscil- 

 lariceae, Chroococcaceae, etc., which contain chlorophyll. 

 Leuconostoc (Van Teigh) has already been mentioned as an 

 intermediate form. A gap certainly exists between Arthro- 

 sporous and Endosporous forms ; but so far as can be seen 

 the latter stand nearer to the former than to any other group, 

 and the interval which separates them may become 

 narrower with further knowledge. On the other side a 

 connection appears to be indicated between Bacteria and 

 Flagellata." 



Class II.— SchizophycejE. 



The present group includes numerous presumably 

 primordial forms of plant life, agreeing in some respects with 

 the Schizomycetes, but distinguished by the universal pre- 

 sence of chlorophyll, and" in most cases showing a higher 

 degree of specialization. The Schizophyceae are divided 

 into three sections, the Diatomacece., Cyanophycece, and 

 Protococcoidea. 



Diatomacese. 



The chlorophyll is masked by a brown colouring matter, 

 and the organic substance of the cell-wall is hardened with a 

 deposit of silica or flint. The species, which are very 

 numerous and very minute, are unicellular, and the cell-wall 



