239 
Algal Ancestry of the Higher Plants. 
Pringsheimia and Protoderma (Fig. 1, d), but, in both of these 
cases, the origin from a system of branched threads is plainly 
evident, and this is also quite distinct in the discoid Coleocluetes. 
There are, however, a number of Algae which probably belong 
to this series (many of them not yet properly described), in which 
this origin from a filamentous condition is unrecognisable in the 
mature state. 
Returning for a moment to our original statement as to what 
we may expect to find in the algal ancestry of the higher plants 
(p. 4), it will be seen that the Chaetophorales satisfy all require¬ 
ments, with one exception. They are a group displaying differen¬ 
tiation of the thallus into prostrate dorsiventral and radial upright 
systems ; one genus ( Draparnaldia ) shows a predominant upright 
system, with a distinct main axis and laterals subservient to 
assimilation and reproduction ; a considerable number of forms 
show reduction of the upright system, so that the thallus comes to 
consist largely or entirely of the prostrate portion. The only one 
of our expectations that is not fulfilled is the existence of forms, 
having sexual organs on the prostrate base and asexual organs on 
the upright threads. As regards this latter point it may first be 
noticed that, in the aquatic Chaetophorales, as long as there is a 
properly developed upright system, the reproductive organs are 
usually confined to it; but, with the reduction of the upright 
system, they are relegated to the prostrate base (cp. for instance, 
Coleochcete pulvinata with C. scutata). 
It is, however, among the terrestrial Trentepohliaceae that we 
meet with the most important indications in this connection. In 
the genus Trentepohlia the zoosporangia are pedicellate, being 
provided with a stalk-cell of a characteristic knee-like form (Fig. 1, 
/), whilst the gametangia are sessile (Fig. l,g). The two kinds of 
reproductive organs are, therefore, readily distinguishable, but it 
should be added that it is not yet certain that these structures are 
definitely asexual and sexual respectively in all the species of the 
genus; in several, however, this has been established beyond doubt, 
and it is to be presumed that it obtains in most, if not in all cases. 
In many species both kinds of reproductive organs are borne on the 
upright system, but especially in those forms in which the base is 
strongly developed, the gametangia tend to arise from the base 
(Fig. 1, g), whilst the sporangia are found on the upright threads 1 
(Fig. 1,/). Very good instances are afforded by T. diffusa , De 
1 Oltmanns, Morph, u. Biol. d. Algen, I, 1904, p. 252. 
