SECT. n. 



VARIATIONS IN RHODOSPERMS. 



243 



in being elliptical, and in the Kytiphlsea pinastroides 

 they are cellular bodies, without any investing mem- 

 branes, clothed with delicate hairs. 



The form of the Khodosperms, as well as the limits 

 of the species, like those of other Algae, are affected by 

 many circumstances known and unknown, such as the 

 depth, temperature, saltness, and currents in the water. 

 The Grelidium corneum varies to such an extent that its 

 forms may not only be considered as distinct species, 

 but even as belonging to different genera, The De- 

 lesseria alata is 

 sometimes desti- 

 tute of its mar- 

 gin, and then 

 its midribs alone 

 being left, it has 

 the form of the 

 Delesseria an- 

 gustissima. Se- 

 veral. species of 

 the florid Algae, 

 which in their 

 natural state 

 have the tips of 

 their fronds even and straight, occasionally produce 

 hooked and clasping tips. 



Brackish water is often a cause of change. The 

 Irish moss, Chondrus crispus, when exposed to the 

 fresh water of an estuary acquires great breadth and 

 thickness, while at low water mark it is thin and 

 has narrow forked branches, and there are many inter- 

 mediate forms. The fruit rarely varies with these 

 changes ; its disposition and intimate structure, as 

 well as that of the frond, are the points of prime im- 

 portance for the determination of genera and species 

 in the Algse. 





