82 Transactions British Mycological Society. 
latter in morphological construction. The envelope can be 
readily separated from the protoplasts, whilst in the Cyano- 
phyceae violent plasmolysis is necessary to effect this. The 
breaking of the membrane into concentric layers is also a feature 
in which Leuconostoc differs from the Nostocaceae and the 
majority of other algae. Unlike the higher Cyanophyceae Leu- 
conostoc possesses no individual cell-sheath. In this, as in its 
occasional cell divisions in two planes, Leuconostoc approaches 
the Chroococcaceae more closely than the Nostocaceae. On the 
other hand the chemical constitution of the envelope is not that 
of any of the Cyanophyceae, nor of the Tetrasporales or Hetero- 
capsales. The chemical nature of the envelope is undoubtedly 
an important systematic character, being not only of specific 
value, since observations on Leuconostoc mesenteroides itself 
show the actual constitution of the envelope to be more constant 
than its form or degree of development, but also of much higher 
taxonomic importance in view of the fact that the nature of 
the membrane substance and of metabolites in general is dis- 
tinctive in the wider groups (orders, classes) of Thallophyta. 
In their report in 1920 on the classification of the bacteria 
a committee of the American Society of Bacteriologists (zx) place 
the genus Leuconostoc in the tribe Streptococceae in the family 
Coccaceae. According to Orla-Jensen(6) Leuconostoc, which as 
already mentioned he includes in his genus Betacoccus, is to be 
placed in the lactic acid bacteria which embraces, besides many 
Coccaceae, a number of rod-forms. 
Leuconostoc mesenteroides has often been associated with the 
genus Streptococcus and by some writers is included in the latter. 
The Gram-reaction may perhaps be a distinguishing feature, 
although the precise systematic value of this character is hard 
to estimate. It is not absolutely constant for given species 
amongst the Coccaceae. It might be suggested that the Gram- 
reaction in the cells of Leuconostoc would frequently be hindered 
by the presence of the secreted mucilage. But some Nostocaceae 
possessing equally developed envelopes on staining for com- 
parison with Leuconostoc show the typical positive reaction. 
Incidentally it may be mentioned that the species of Cyano- 
phyceae are very variable with respect to the Gram-reaction so 
that it has no importance as a group character. 
The majority of species of Streptococcus are parasites, but 
there are considerable biochemical similarities between the two 
genera as has been shown by Orla-Jensen(6). The latter in- 
vestigator has also shown that Streptococcus and, in fact, all the 
bacteria falling in his group of lactic acid bacteria produce 
capsules during the early stage of development of the colony. 
On the other hand Leuconostoc, in its sheathless form is quite 
