PH^EOPHYCE^E 61 



Stcechospermum, and Spatoglossum is erect, flat and 

 frondose, dichotomously branched, and attached at 

 the base to the substratum by root-hairs. In several 

 species of Zonaria the frond is procumbent and on 

 its lower surface attached at many points by root- 

 hairs to the surface. Padina has a procumbent 

 thallus, but in its ultimate parts assumes a tendency 

 to the upright habit. Dietyopteris alone has a mid- 

 rib. The dichotomy of Didyota follows the longi- 

 tudinal division of the apical cell, while in the other 

 genera the meristematic group divides into two at 

 the point of divergence. The external layers, by re- 

 peated transverse and longitudinal divisions, develop 

 an epidermis of numerous small cells, rich in chroma- 

 tophores, while the internal cells remain large and 

 almost colourless and undergo rare and irregular 

 division. The paraphyses have a basal growth, and 

 occur in tufts or in rows in symmetrical fashion. 



The Reproductive Organs occur always on peculiar 

 individual plants. In Didyota and Taonia the 

 plants are unisexual; in Padina both oogonia and 

 antheridia occur on the same plant ; while in all 

 cases the non-sexual spores occur on plants which 

 do not bear other reproductive organs. All three 

 kinds of reproductive bodies are of similar origin. 

 An epidermal cell becomes enlarged and projects 

 slightly, then divides transversely, the upper portion 

 being the mother-cell of the reproductive body, 

 while the lower remains part of the vegetative body. 

 The organs designated oogonia are united in a dense 

 sorus of such cells as have been described, the con- 

 tents of the reproductive cells remaining undivided 



