200 E E. Fritsch 



it is not wise to conclude from experiments under laboratory 

 conditions that such forms will be able to grow and multiply 

 when buried in the soil, although it may well be that at certain 

 times conditions for active growth may obtain. 



For diverse reasons I am inclined to believe that the subter- 

 ranean Algae are in large part, if not entirely, surface-growing 

 forms that are washed down into the soil by heavy downpours 

 of rain. Thus buried, they may perhaps occasionally find the 

 necessary means of sustenance and so multiply for a time, but 

 I think it is at least doubtful whether there is any marked activity 

 on the part of such subterranean forms. It is significant in this 

 connection that the most frequent of the subterranean Algae are 

 known to be common surface forms (see also the occurrence of 

 moss protonema), and are unicellular types with rounded cells 

 {Chlorococcum) or filamentous forms that readily fragment into 

 short lengths {Hormidium, Stichococcus). It is also significant 

 that common filamentous surface forms that do not show such 

 ready fragmentation {Prasiola, Zygogonium ericetorum) y so 

 far at least, have not been recorded beneath the soil surface. 

 It is curious, however, that the soil-inhabiting Mesotaeniaceae 

 (species of Mesotaenium and Cylindrocystis) hitherto have not 

 been found in subterranean habitats. Esmarch^'' also arrived at 

 the conclusion that the subterranean Blue-green flora is com- 

 posed of the same forms as occur at the surface. Here the capa- 

 city to propagate by motile hormogones and the known liking 

 for saprophytic nutrition on the part of these forms will no 

 doubt tend to lead them to a direct penetration from the surface 

 into the upper layers, as apparently occurs especially in cultivated 

 and in calcareous soils. 



As to the Algae mentioned above, that so far have rarely or 

 never been found except in cultures of soil samples (Gongrosira 



