99 
On the Retention of Vitality by Algce. 
hear on their surface the denticulations that are characteristic of 
the species, hut in the majority these are suppressed to a greater 
or less degree, and every gradation can he observed between the 
typical form and a form with almost smooth walls. Many of the 
cells enter into a palmella state; a number of the cells also tend 
to assume a much larger size than is typical, hut these differences 
are probably due only to the conditions under which the alga is 
growing, and there is no reason for considering that it is a different 
species. 
The alga has been obtained from the following soils : Agdell 
1867, Barnfleld 4870, Hoosfield 1868 ; its resting-cells have thus 
germinated after nearly fifty years. 
Chlorococcum humicola (Naeg.) Rabenh. 
This alga, as observed in soil-cultures, exhibits a far more 
complicated life-history than has previously been thought to he 
the case ; it forms the subject of a separate paper that is in course 
of publication by the Linnean Society, and further details are 
therefore unnecessary here. It has been obtained from all of the 
plots examined, and is able to retain its vitality for at least sixty 
years. 
Stichococcus bacillaris Naeg. 
The form of this alga obtained from the cultures differs in 
no way from the typical form. It was observed in the Barnfleld, 
Agdell and Broadbalk soils, hence the maximum time after which 
it has developed is forty-eight years. 
C. Mvxophycb/E. 
Nostoc muscornm Kiitz. 
Forms of this alga have appeared from all the Broadbalk 
samples, with the exception of that collected in 1865, and also 
from the Hoosfleld sample. It has retained its vitality for nearly 
seventy years even under conditions of extreme drought. The 
forms obtained from the different samples, though agreeing in 
mode of growth and in general characters show considerable 
variation in details. In certain of the cultures, notably in those 
of the 1893, 1881, and 1868 Broadbalk samples, the form observed 
agrees almost entirely with the description and dimensions given 
by Lemmermann, the chief difference being that the spores are on 
the whole rather smaller, rarely exceeding 7-8/x in length. Lem- 
