2 8 



forma pusilla. 



Plant smal! ; joints slightly calclfied, compressed, tridentate, not very deeply cut, or sub- 

 cylindrical (fig. 44). 



forma rotunda. 



Plant slightly calcified; lowest joints simple, cylindrical, all other joints semicircular or 

 discoid, indistinctly ribbed (fig. 45). 



H. incrassata is almost as variable a plant as H. Opitutia and its forms have been 

 desenbed as several distinct species, as is seen by the list of synonyms above. 



The type specimen of H. incrassata [Corallina Ellis and Solander) has unfortunately 

 been lost. but the excellent figure given (Eli. et Sol. Nat. Hist. Zooph. 1. c.) leaves no doubt 

 as to the form of the plant designated by this name. Specimens of it are common in most 

 herbaria and an examination of the mode of fusion in the central strand shews the pits 

 described and figured under H. incrassata by Dr. Askexasy (1. c). The pits in this species 

 are smaller than those of H. inacroloba, but they vary in size. In some forms, notably forma 

 ovata, the pits are often either wholly wanting or are so small that they are only made visible 

 by careful staining. This partial or entire absence of pits may however occur in other forms 

 of H. incrassata, though it has only been seen in stunted plants with small joints : which is 

 cause and which effect it is difficult to say. It may be argued that in a classification founded 

 on the mode of fusion of the central filaments, it is illogical to class together as one species 

 plants in which the filaments communicate by means of pits, and plants in which the filaments 

 neither fuse nor communicate at all. But among the specimens of H. incrassata, to which 

 I have had access, there have been plants representing all gradations of this character from 

 filaments with well-developed pits to those which were entirely free and shewed even no tracé 

 of thin places on their unusually thick walls (fig. 47). Thus it was obviously impossible to regard 

 those plants, in which the central filaments are free at the apex of a joint, as anything more 

 than a form of growth of H. incrassata. This internal variation is most often found in small 

 tufted plants from the Pacific Ocean, corresponding in outward form to Prof. J. G. Agardh's 

 var. ovata. Unfortunately it was impossible to obtain the original plant of var. ovata for exami- 

 nation, but a photograph of it, natural size, was most kindly sent me by Professor Nordstedt, 

 which shews that at least in outward form my Pacific plants with free central filaments correspond 

 with var. ovata. Plants shewing entire or partial absence of pits occurred among the " Albatross" 

 collections; in a markedly trilobed form approaching forma Lamourouxii in the " Siöoga" 

 collections: and in two plants from Funafuti, which come under A. 21 in the paper referred 

 to above. It was also interesting to find that the type specimen of H. Opuntia var. macropus 

 Ask. kindly lent me by Professor Engler shews small and few pits in the central filaments, 

 combined with the external characters of forma typica, namely, the thick base and trilobed 

 upper joints. The plant is however small and stunted. 



The type specimen of IJ. inonilc {Corallina mouilc Eli. et Sol.) is also missing, but an 

 examination of plants, corresponding in external form with the Solander figure, shewed well- 



