AFFINITIES AND CLASSIFICATION OF ALGE. 61 
is obscure; but they must probably be regarded as descended, 
through many removes now lost, from the Coleochztacex. The 
Muscinew are regarded by Goebel as probably derivatives from 
the Characew; and this seems the most likely hypothesis ; though 
a difficulty is presented in the relationship of the Hepatice, 
especially the thalloid forms, to the more highly developed Musci, 
unless the former are regarded as a retrogressive offshoot from 
the latter. Another possible line of descent of the Muscineæ 
has been indicated, from Lemanea or similar forms. 
Another great gap, in which many connecting links must have 
been lost, occurs between the Muscine® and the Vascular Cryp- 
togams. It is difficult to regard the Vascular Cryptogams as 
descended directly either from the Characex or from the Mus- 
cines. The construction of the vegetative apparatus in the 
Equisetacew among the former reminds one, to a certain extent, 
of that in the Characex. In its general features the mode of 
sexual reproduction has now become established, to undergo, in 
Flowering Plants, one more change, in the substitution of 
motionless pollen-grains with their pollen-tubes for motile 
antherozoids. From the Selaginellacee among Heterosporous 
Vascular Cryptogams, it is comparatively plain sailing, through 
the Gymnosperms, to the Angiosperms. 
LINN. JOURN.—BOTANY, VOL. XXIV. 
