28 
William J. Hodgetts 
production. The form was much influenced by competition with 
other filamentous Conjugates in the pond. In the case of M. viridis 
abundant bright sunlight does not seem to be so essential for 
conjugation as with M. scalaris, and it is also adapted to lower 
temperatures. 
The Desmids of the pond (Section IX), as regards the position 
of their maxima, tend to fall into two groups, (i) those which have 
their maximum in spring or autumn ( Hyalotheca dissiliens, Sphcero- 
zosma granulatum, Closterium acerosum), and (2) those which attain 
a maximum in summer or early autumn ( Closterium moniliferutn, 
Cl. Kiitzingii, Cl. lineatum, Pleurotcenium Ehrenbergianum, Cos- 
marium Botrytis, Staurastrum brevispinum, S. Dickiei, and others). 
Closterium striolahim tends to connect the two groups. Those of the 
first group prefer moderate temperatures (usually a monthly mean 
between 6° and 13 0 C.) and rather moderate concentrations (between 
10 and 18 degrees); those of the second group are adapted to higher 
temperatures (a monthly mean between io° and 16 0 C.), and some¬ 
what higher concentrations (between 14 and 21 degrees, although 
differing slightly with the different species). 
The three species of Staurastrum were more tolerant of higher 
concentrations (up to 27 degrees) than the Cosmarium spp. The 
Desmids of the pond which have conjugated fall into two classes, 
(1) those which require abundant bright sunshine before conjugation 
can take place ( Closterium acerosum, Cosmarium Botrytis), and (2) 
those which are able to conjugate given only a moderate amount of 
sunshine ( Staurastrum brevispinum, S. Dickiei, Closterium lineatum, 
Cl. rostratum). 
The species of CEdogonium (Section X) present in the pond fall 
into two groups; (1) includes a wide sterile species which attains a 
great maximum during June—August, and (2) narrower species 
( 0 . cryptoporum, 0 . crispum, 0 . Borisianum, 0 . Braunii, 0 . echino- 
spermum, and 0 . rugulosum) which were at a maximum in May (or 
early June), and rapidly declined in June after fruiting. The wide 
sterile species of the first group is favoured by the higher summer- 
temperatures (a monthly mean between 12 0 and 16-5° C.), and no 
relation is shown towards bright sunshine, and little to the con¬ 
centration of the water. The narrower species of group 2 are typical 
spring-forms favoured by a monthly mean temperature between io° 
and 13-5°, the higher temperatures being unfavourable; and their 
maxima always occurred after a period of very sunny weather, which 
supports the view that abundant sunshine is essential for oospore- 
