AFFINITIES AND CLASSIFICATION OF ALG X. 59 
In this family there is still no great advance in vegetative struc- 
ture, and we have an evident connecting link with (Edogonium 
in Bulbochete. In the typical genus Coleochzte we find, in the 
non-reproductive part of the thallus, a singular change from a 
filament to a simple plate of cells, adapting it to its mode of 
growth, as a flat disk attached to the surface of water-plants. 
The mode of sexual reproduction has, however, attained a much 
higher degree of complexity. The oogone is surmounted by a 
tubular appendage, the trichogyne, through which the motile 
antherozoids find their way to the oosphere in order to impreg- 
nateit. The fertilized oogone then becomes invested by a cortical 
layer of cells, forming the complex body known as the sporocarp. 
The microscopic family of Pediastree so closely resembles the 
Coleocbstaces in some points, and is so difficult to locate else- 
where, that I find it hardly possible to regard it in any other 
light than as a degraded type of this family in which every trace 
of sexual reproduction has been lost. Many authorities place 
Pediastrum among the Protococcacew, others associate it with 
Hydrodietyon ; with the latter genus it seems to me to have 
scarcely anything in common; in no true sense of the word do 
its cells constitute a ccenobe. 
The Coleochztacex lead us up directly to the highest type of 
structure attained by Thallophytes, the Red Seaweeds or Floride, 
a well-defined and natural group, though exhibiting remarkable 
variety in the degree of development of the sexual organs. So 
striking is the resemblance in the mode of impregnation in the 
most highly developed genera of Floridez, such as Callithamnion, 
Dudresnaya, or Corallina, to that in Coleochste, that it is scarcely 
possible to doubt the direct descent of one from the other. In 
addition to the acquisition of a red pigment, the chief difference 
consists in the replacement of motile antherozoids by motionless, 
or at least not actively motile, male elements known as “ sper- 
matia.” The process of fertilization is the most complex which 
occurs among Thallophytes, and presents a remarkable forecast, 
80 to speak, of the mode afterwards elaborated an Flowering 
Plants, but only after a very long interval comprising the entire 
evolution of Muscine® and Vascular Cryptogams. It is instruc- 
tive to note that with the loss of motility of the male reproduc- 
tive bodies is correlated the loss of motility also of the non-sexual 
reproductive bodies or tetraspores. Another possible line ot 
descent of the Florides has already been indicated, from the 
