428 Ecology 



normally in the vernal phase. In temperate areas Mougeotia viridis is 

 almost invariably the first species to enter into the fructiferous condition in 

 the spring (G. S. W., '09 B), beginning its spore-formation in the midlands 

 and southern counties of England in March, with a water-temperature of 

 5__ 7 C., and at higher altitudes in the mountainous areas in April or May. 

 Other Conjugates are represented by certain desmids, of which the following 

 are fairly generally distributed in the ponds and ditches of temperate 

 countries : Olosterium Ehrenbergii, Cl. moniliferum, Cl. rostratum, Cl. ace- 

 rosum, Cosmarium Botrytis, C. granatum, C. Meneghinii, and Staurastrum 

 punctnlatuni ; others, less frequent, are Closterium peracerosum, Cl. acutum, 

 Gosmarium biretum and Staurastrum crenulatum. In larger ponds, and in 

 others which never dry up, many additional species are found, such as 

 Cosmarium reniforme, C. humile, C. Boeckii, Closterium Venus and various 

 others. On the older rocks in the mountainous areas of western Europe 

 roadside ditches and pools very rarely dry up and the species of desmids are 

 often quite different. Cosmarium speciosum, C. decedens, G. pseudarctoum, 

 Euastrum dubiam, Tetmemorus Itevis, Arthrodesmus Incus and many others 

 make their appearance. 



In the tropics species of Spirogyra are quite as abundant as in temperate 

 regions, but there is a striking absence of the narrower species with the 

 replicate or infolded extremities of the cells (Fritsch, '07 A and v, ; G. S. W., 

 '12). It is also a noteworthy fact that Sp. decimina is much the commonest 

 species. The desmids are for the most part essentially different from those 

 of temperate areas. 



The genus Microspora is well represented in temperate countries, most of 

 the species being decidedly spring types, although some of them occur in 

 considerable quantity in the late autumn. Vegetative filaments of these 

 species never entirely disappear in the summer from the waters of those 

 ponds and ditches in which they occur. The investigations of Fritsch & Rich 

 ('13) confirm the view that the genus as a whole is a cold-water type and a 

 very vigorous one. In tropical countries Microspora is principally an upland 

 type occurring in mountainous areas up to 8000 or 9000 ft. M. amcena, 

 which is the largest species, thrives best in running water although it may 

 occur in ditches. 



One or two species of Cladophora occur in ponds, generally where there 

 is good aeration of the water, but as a rule species of this genus require more 

 aeration than can be obtained in very small bodies of water. Rhizoclonium 

 hieroglyphicum may occur in very stagnant ponds, this species being able to 

 adapt itself to almost every kind of environment. Pithophora is almost 

 exclusively tropidal and subtropical, replacing to some extent the genus 

 CladopJiora, in the smaller sheets of water. Fritsch ('07 A) considers Pitho- 

 pltora, with its comparatively thin cell-walls, as better suited than the other 



