88 
Review. 
finally the characteristic motile form with two unequal flagella—serve 
at once to convince us of the natural character of the scries and to 
extend the generalisation that constancy in cytological character is 
one of the most important of morphological features and therefore 
one of the most important marks of affinity in the Algae, and should 
entirely overrule similarity of conformation and habit of the thallus, 
and even resemblance in the form of reproduction. This general¬ 
isation was already well established in regard to the pure green, 
unicellular and colonial forms, while among the Heterokontze we 
have a series of organisms ranging from Chloramceba , a naked, 
flagellate, amoeboid form, through unicellular types which shew an 
increasing preponderance of algal features, to coenocytic forms like 
Botrydium, and multicellular filamentous forms like Conferva, 
(recently found to posses motile anisogametes). A striking peculiarity 
of the Heterokontze, as opposed to the pure green series, is the 
apparent rarity of gamogenesis, which has not reached anything like 
so high a stage of evolution as in the latter. Professor Oltmanns 
does not follow Bohlin in transferring the Vaucheriaceze to the 
Heterokontan series, and his decision is perhaps scarcely to be 
wondered at. Nevertheless the traditional position of Vaucheria 
among the Siphonales is certainly not satisfactory. With the 
exception of the formal resemblance given by the fact of its thallus 
consisting of a branched coenocytic tube, a resemblance on which 
we can lay scarcely any emphasis in the absence of other evidence 
Vauclieria scarcely presents a single character in common with the 
other Siphonales. Pyrenoids and starch are absent, and the 
method of reproduction, both in the highly differentiated sexual 
process, and the curious and unique synzoospores, has no parallel 
whatever in the other families. Ernst’s recently described 
Dichotomosiplion, which forms starch and has traces of internal 
ring-walls at the bases of the branches, but which in respect of 
its reproduction is undoubtedly a Vaucheria , does certainly take us 
some little way towards bridging the gulf, a gulf that nevertheless 
remains sufficiently wide. On the other hand we have a resemblance 
to the Heterokontze in the absence of starch and presence of an oil 
in Vaucheria itself, while the antherozoids of the latter, with 
their often unequal, and laterally inserted flagella, seem to work in 
very well with the Heterokontan type, though the cilia of the 
Vaucherian synzoospore apparently fail to concur. On the whole 
we incline to a belief in the Heterokontan alliance, though 
Dichotomosiplion slightly weakens the case for such an affinity. Our 
