frond is usually simple and flabelliform, infundibuliform, sometimes proliferous or 



ternal form is subject t>> variation in most of the spe- 

 en concentrically zoned, and sometimes longitudinally striate or rugose, 

 but both these ch ar from stable. The colour of dried specimens may be any 



shade from hy-white. I h<- margin, or even the frond itself, maj be mon or 



ut this is probablj often the result of external influences, such as wave- 



ilcification. All the species ol Udotea^ .is here defined, are calcified, some spei 

 much more than others, e g. U. flabellum is thickly encrusted, while U. indica is thinly 

 speaking the species maj be divided into two groups in regard to calcifica- 

 i those in which the filaments of the frond remain obvious, as in U. orientalis 



etc, where they have the appearance of being separately 

 d with a thin layer ol calcium carbonate; 2) those in which the mairt filaments become 

 entirely concealed, as in U. argentea, U. flabellum ^ etc, where the filaments and their lateral 

 appendages become involved in one common mass of incrustation. 



In the first group, the calcareous sheath of the filaments is seen to 1"- porose, just as 



in Penicillus compare fig. 182). The pores are variable in size and distribution even in the 



same plant. What is the meaning of these pores? They can scarcely be regarded as windows 



for the more efficiënt illumination of the interior of the filament, since the calcareous sheath 



is already so thin and translucent as to offer little hindrance to the passage of light. In all 



probability their distribution corresponds with that of the green chromatophores inside the 



filaments. and they themselves mark the spots where bubbles of oxygen were evolved during 



the photo-synthetic process of the plant. Presumably the deposition of calcium carbonate would 



ted at the time of photosynthesis only and naturally could not occur at those points 



where bubbles of gas were clinging to the sides of the filaments. It will doubtless be objected 



that the chromatophores, owing to the streaming movement of the protoplasm, would not 



in stationary long enough to lay down even the foundations of the pores. But we would 



point out that at and near the growing apices of the filaments the protoplasm is usually densely 



congi uniek, in the very region where the thin porose calcareous sheath first begins 



to be visible. Thus there is a stasis of the protoplasmic circulation at the young ends of the 



filaments. which appears to be sufficiently prolonged for the mapping out of the young pores. 



The pores, thus initiated, doubtless become permanent, since they would naturally provide the 



outlets for the oxygen-bubbles. In these plants of the first group the starch is found 



1. not in the well-illuminated main filaments of the frond, but in those of the thickly 



and hence dark 1 stipes. 



In the second group, on the other hand, abundant starch is found stored in the main 



of the frond (as in U. flabellum\ indicating the darkness of the interior ol the fr< 



the thick encrustation. The question arises how in this case is sufficiënt illumination 



the formation of this large store of starch. The answer to this question is 



inyone when the calcified surface is submitted to examination under a low power of 



diameters,. The surface is seen to be pitted with innumerable "pores which 



