Caulerpacese 



231 



Fig. 151. A, longitudinal section of the 'leaf 

 of Caulerpa prolifera (Forsk.) Lamx., tt, 

 transverse trabeculae ; It, longitudinal trabe- 

 culte; x about 80 (after Oltraamis). J5, trans- 

 verse section of ' stem ' of Caulerpa Holmes- 

 iana G. Murray, x about 40 (after G. Murray). 



chloroplasts, which are without pyrenoids, are according to Mme ,Weber van 



Bosse in some species relatively large. 



The peripheral layer of protoplasm is 



for the most part quiescent, but the 



more central anastomosis exhibits an 



upward and downward streaming 



movement which caused Janse ('90) 



to regard the streams as nutritive 



in character. 



There are no reproductive organs 

 in Caulerpa, propagation taking place 

 only by the separation of proliferous 

 shoots. This is very well seen in 

 Caulerpa prolifera, a species which is frequent in the Mediterranean, 

 preferring deep water and sheltered places. It has been shown that in 

 shallower, more turbulent water the proliferations are more abundantly 

 developed. 



The genus Caulerpa is divided into twelve sections based upon the type of habit, 

 which resembles that of mosses, lycopods, ferns, Zostera, sedums, cacti, etc. Thus, there 

 are the sections Charoideae, Bryoidese, Filicoidetc, Zosteroidese, Sedoidese, etc. Almost 

 all the types of habit exhibited by higher plants are found to exist in this extraordinary 

 genus. The genus was monographed by Muie Weber van Bosse ('98) and systematic and 

 ecological studies have been published b'y Svedelius ('06 ; '07). It is to Borgesen ('00 ; '07), 

 however, that we owe the splendid knowledge we now possess of the general biology of 

 this genus. Borgesen has shown that Reinke's views ('00) that species of Caulerpa live 

 under uniform external conditions and that they show no adaptations are not at all in 

 agreement with facts. 



Borgesen recognizes three ecological types in which the mode of growth as a whole 

 depends upon environment. 



(1) Epiphytic or mud-collecting Caulerpas. One of the best examples is C. verticillata 

 (fig. 149), in which the rhizomes are almost thread-like and form a dense mat on the 

 roots of Mangroves, accumulating mud and fine organic detritus. 



(2) Sand and mud Caulerpas. Exemplified by C. crassifolia (fig. 150), C. cupressoides, 

 C. taxifolia, etc., which are found in sheltered places in shallow water and in deeper water 

 (down to more than 100 feet) where the influence of the surf is not felt. The rhizomes 

 are strong and vigorous, growing extensively over a loose, sandy or muddy sea-bottom. 

 In this way C. prolifera covers large areas of the soft bottom of parts of the Mediterranean. 

 Borgesen likens the growth of Caulerpa cupressoides to that of Carex arenaria, the 

 awl-shaped end of the rhizome boring its way through the sand in perfectly straight lines 

 often more than a metre in length, and sending up at short distances the erect 'foliar 

 shoots.' At about the same distance from one another as the erect 'shoots,' vigorous 

 ' roots ' grow down into the sand, undivided for about 2 or 3 cms., but then repeatedly 

 branched to form numerous fine rhizoids which are firmly fastened to the sand and gravel. 

 A similar attachment is found in Penicillus. Halimeda (consult fig. 154) and Udolea 

 (three genera belonging to the Codiacese) when these Algae are growing on a loose bottom, 

 the loose material being knitted together so as to replace a fixed substratum. 



