260 Siphonodadiales 



It seems likely that the Cladophoracese have originated from the Valouiacese and not 

 improbably from the Boodleae through such a genus as Cladophoropsis. Wille's division 

 of the family into the Cladophoreae, Chsetoinorphese and Rhizocloniese is the best arrange- 

 ment which has yet been suggested, but his inclusion of Cladophoropsis in the Cladopho- 

 racese is not quite in keeping with our present knowledge of the genus, Borgesen having 

 recently shown that it is most nearly related to Boodlea. The view that the Cladophorese 

 is the sub-family from which the other members of the Cladophoracese have evolved is 

 supported by strong evidence ; and, if it be a correct^ interpretation of the facts, then it 

 follows that the small sub-families of the Chsetomorphese and Rhizocloniese are rather 

 specialized groups, the former having arisen by a suppression of branch -formation (the 

 relics of which can be seen in Urospora), and the latter by a reduction of the bi-anching 

 and of the size of the coenocytes, which has been accompanied by a corresponding 

 reduction in the number of nuclei. 



CLADOPHORACE^ 



Cliidophnrupsis 



ROODLE/E 



Boodlea 

 VALONIACE.E 



The above diagram illustrates the possible relationship of the Cladophoracese with the 

 Valoniacese. 



Oltmanns' extension of the scope of the Cladophoracese ('04), in which he included the 

 genera Anadyomene and Microdictyon, forms, as pointed out by both Wille ('09 B) and 

 Borgesen ('13), scarcely a natural group. 



Sub-family CLADOPHORE^:. The leading feature of this sub-family is the 

 richly branched thallus, which may be the growth of a single individual or of 

 several individuals in which the branches have become inextricably inter- 

 woven. The branches only rarely develop anything of the nature of ' tenacula ' 

 and therefore never form a connected net-like thallus such as occurs so 

 frequently in the Valoniacea?. 



On the germination of the zoogonidium or of the zygote there is from the 

 very first a differentiation of the thallus into a cauloid part and a rhizoid part. 

 The latter usually 'consists of a few basal segments, but it may consist of a 

 strong hold-fast resulting from the growing together of a number of rhizoidal 

 filaments, as in Cladophora rupestris. Other rhizoids, which are developed 

 from the cauloid part of the thallus, may be described as accessory rhizoids. 



