CHLOROPHYCEA 163 
been made quite clear by Mrs. Weber van Bosse that 
certain forms of Spongocladia are mere growth-forms 
of Struvea delicatula, transformed by this remarkable 
association with a sponge. This proof has a further 
interest as regards Struvea. No reproductive organs 
of Struvea are known, but Areschoug, who originally 
described Spongocladia, has figured what appear to 
be zoospores germinating in si¢w within the filaments 
of S. vaucherieformis. 
In Microdictyon we have similar net-like fronds, 
but without a stalk. The frond, which is of prostrate 
habit and of indefinite margin, is attached by short 
rhizoids. A closely-allied genus, Boodlea, instead of 
forming a flat network, has branches running indefi- 
nitely in all directions, each branch bound to its 
neighbours by haptera like those of Struvea. We have 
therefore a sort of network extending in all directions, 
and not in one plane like Microdictyon and Struvea. 
In Anadyomene the flat thallus recalls Struvea in 
being traversed by main branches, but the spaces 
between these are wholly filled with the cells of 
lateral branches, and there is therefore no network. 
Though the thallus of Dictyospheria, for example, 
may be utterly unlike such a form as Strwvea in 
habit, there is in reality very little dissimilarity in 
structure. The binding of the cells together by 
haptera to form a tissue is common to both extreme 
forms; in the one case the cells remain isodiametric 
and unbranched, in the other they are more or less 
elongate and definitely branched. 
The Reproductive Organs.—Zoospores are produced 
in Valonia, Siphonocladus, and possibly in Microdictyon 
M 2 
