Johnson — Callosities of Nitophyllum versicolor. 157 



the entanglement of the cellular filaments of the callosities in the 

 mud, &c., of the sea bottom, and the absence of the usual reproductive 

 organs of the Florideae, I think there is everything to indicate that 

 the callosities are organs for the vegetative propagation of the 

 plant, functionally comparable to the gemmae of a Liverwort. A 

 plant of N. versicolor of one season dies down, the callosities, well 

 protected by their thick-walled superficial cells, lie dormant, to 

 develop in the following spring into new plants. The cellular 

 filaments of the callosities (of which filaments there are traces on 

 the root) serve to give anchorage. In the process of germination 

 the food matter stored up in the callosity is used up, leaving the 

 emptied cells of the stalk. 



Affinities. — Greville, in the Scottish Cryptogamic Flora^ con- 

 sidered our plant a form of Delesseria Bonnemaisoni, Ag. In the 

 Algse Britannicse^, Grreville altered his opinion so far as to place 

 N. versicolor in the species Nitojjlixjllmn Gfuelini, Grrev. It seems 

 to me, in the light of the knowledge just gained of the nature 

 of the callosities, that JSf. versicolor is in reality not a distinct 

 species, but a gemmiferous state of Nitoplnjllum Gmelini or N, 

 Bonnemaisoni. Judging from the description and illustration by 

 Batters of the form crassinerva^ of N. Bonnemaisoni, Grrev., I believe 

 we have a strong indication in it of the closest connexion between 

 N. versicolor, Harv., and JV. Bonnemaisoni, Grev. 



The structure of the callosities of iV. versicolor has an important 

 bearing on the structure of the thallus of the Floridese in general. 

 Schmitz^ considers the thallus of a red alga to consist of a system 

 of branching filaments, each filament growing by means of an 

 apical cell from which segments are cut off in succession by the 

 formation of horizontal walls. New filaments arise by a kind of 

 budding, an irregular apico-lateral division of a parent cell, the 

 cell so cut off becoming the apical cell of the new filament. The 

 segments cut off from the apical cells never divide into two by a 



1 E. K. Greville : Sc. Crypt. Fl. s. 6, PI. cccxxir, figs. 2 and 3. 



2 E. K. GreviUe : Alg. Brit. p. 81. 



3 E. A. L. Batters : List of Berwick Algse, PL xi. fig. 12. 



'■ F. ScLmitz : " Untersuch. ii. d. Befruchtung d. Florideen 1883." (See transla- 

 tion by W. S. Dallas in Ann. Mag. Kat. Hist. vol. xiii. 1884.) 



