CHLOROPHYCE^E 1G3 



been made quite clear by Mrs. Weber van Bosse that 

 certain forms of Spongodadw 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 situ within the filaments 

 of S. vauchericeforinis. 



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 Dictyosphceria, for example, 

 may be utterly unlike such a form as Struvea 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 



