A Igae and the Principles of their Evolution. 1 1 3 
regularly disposed, and the number of the cell-rows also is 
determinate. With the gradual evolution in the external 
morphology, the thallus of the marine species becomes very 
definite, and in some cases, like Enter omorpha , active apical 
cells play a predominant part in the development of the new 
tissues. Through the genus Mono stroma 1 , and especially 
through the fresh-water species, the Ulvaceae are closely 
connected with Tetraspora. The disposition of the cells 
dividing at right angles, above described in the Volvocineae 
and Palmellaceae, is here also of very common occurrence. 
With regard to the early development, there are several very 
variable modes. The young thallus may take a globular, 
tetrasporoid, or shortly filamentous shape. The Palmella- 
condition is also found under certain circumstances in Mono- 
stroma , and resting cells with thick cell-walls are very easily 
formed, as in the Palmellaceae. The production of macro- 
and micro-gametes or zoospores takes place in the same 
manner, and isogamy is quite as frequently observed. There 
can be no doubt, therefore, about the close affinity of the 
Ulvaceae to the Palmellaceae. 
The same may be said of the Chaetophoraceae, which 
constitute another group. The polymorphism of Stigeoclonium 
is well known 3 ; this Alga with its branched filaments can 
assume a Palme lla-cond\X\on 4 , and in every stage of its life 
exhibits some very striking modifications. The adult plant 
consists of a rhizome with branched filaments and swollen cells, 
from which rhizome arise further branched filaments terminating 
in hairs. But the ramifications are very inconstant, and con- 
sequently the different species have not been distinguished 
with accuracy. Each of the cells can separate 5 from the 
1 Chodat, Monostroma bullosum , Soc. Bot. France, loc. cit. 
2 Reinke, Ueber Monostroma bullosum , & c. Jahrb. f. Wissensch. Bot. II, 
p. 331, 1878. 
3 Famintzin, Die anorganischen Salze, Bull, de l’Acad. Imp. des Sc. St. Petersb., 
XVII, p. 31. 
4 Cienkowski, Zur Morphologie der Ulothrichien, Bull, de l’Acad. Imp. des Sc. 
St. Petersb., XXI, 1876. 
5 Chodat et Huber, Remarques sur le systeme des Algues Vertes, Archives des 
Sc. Phys. et Nat., Geneve, 1894, p. 395. 
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