The Classification of the Algae. 
89 
author’s account of the many existing observations on the structure 
and behaviour of this curious group is excellent and interesting, though 
we note that Davis (Bot. Gaz. Vol. xxxviii., No. 2,1904) has contradicted 
his account of oogenesis, affirming that of the numerous nuclei 
present in the yonng oogonium all but one are destroyed instead 
of wandering back into the parent tube. Davis’ version certainly 
seems a priori more likely to be correct, but we ought to wait 
for confirmation of one or other of the accounts before we can 
regard the matter as settled. 
Perhaps the most important consequence flowing from the 
establishment of the series of Heterokontae is the weight which it 
compels us to attribute to the characters of the motile cell as a stable 
morphological feature. YVille had already separated the Conjugate 
from the rest of the Green Algae on very good grounds, and with the 
further break-up of the remaining families according to their 
zoospore-characters, we find the whole of the green forms (excluding 
the Characeae) falling into three great series, separated by numerous 
distinctions of which the most striking is the locomotor apparatus 
of the reproductive cells. The only outstanding exceptions are the 
closely allied genera CEdogonium and Bulboclicete , (with which must 
be associated Stahl’s striking form CEdocladium, described in 1891 
but apparently never seen since), and Derbesia, a siphoneous form 
usually placed close to Bryopsis on account of the strong resemblance 
of its vegetative structure to that of the latter genus. The zoospores 
of Derbesia, however, which were described by Sober in 1847 and of 
which no more recent account is available, are said to resemble those 
of the Qidogoniaceae in possessing a crown of very numerous cilia 
attached round the anterior end, and therefore differ very strikingly 
indeed from the bi-flagellate type, which (with quadri-flagellate 
variations) is universal among the zoospores of the remaining green 
forms. This fact led Bohlin to separate the CEdogoniaceae as a 
special series the Stephanokontae and to be logical, Derbesia should 
go with them. Thus we have four great series of Green Algae, 
Isokontae with two equal flagella, including the great majority of the 
genera, Heterokontae with two unequal flagella, Stephanokontae w r ith 
a crown of cilia, and Akontae with non-ciliated reproductive cells. 
The hypothesis is that each of these series or phyla—at any rate 
the first three—is separately derived from the Flagellata, the 
ancestors of each having the characteristic ciliation. In the case 
of the first two we have actual evidence of such derivation. 
The strength of the case for this view, which has already been 
