158 Scientific Proceedings, Royal Dublin Society. 



vertical or horizontal median wall. Schmitz applies this theory to 

 the whole of the Rhodophycese, the broad leaf-like thallus of a 

 Nitophyllum or Rliodymenia being due to the cementing together 

 of the branching filaments. It will be seen that this mode of for- 

 mation of the thallus is altogether different from that in the higher 

 plants in which true tissues are formed from the meristem by 

 divisions in all directions. So far does Schmitz apply his view 

 that he excludes the group Bangiacese from the Rhodophyceee, partly 

 because their thallus does not conform, in its mode of development, 

 to that of the rest of the Florideee. A comparison of the cross- 

 section of the callosity or stalk of N. 'versicolor with that of the 

 stalk and midrib oi Dictyopteris polypodioides^luQXixx} will show the 

 greatest possible similarity. The production of the thickening of 

 the midrib of the Brown Alga, Dictyopteris, Lamx., is admittedly of 

 a parenchymatous nature, comparable to the thickenings of a 

 Draccena stem, and it seems to me that the thickenings of N. ver- 

 sicolor must be so regarded. Before Schmitz can apply his theory 

 to the whole of the Floridese, and before he can exclude the Ban- 

 giacese, because of their want of conformity to the theory, it will be 

 necessary to explain the apparently anomalous condition of N. 

 ■versicolor, Harv., and the mode of formation of all thickenings of 

 Floridean genera — e.g. the "veins" in other species of Nitoi^hylluni, 

 Grrev., in which there are indications of a parenchymatous nature. 



Summary. 



1. The root of N. versicolor, Harv., is comparable to that of 

 other species of the genus, merely a slight discoidal enlargement 

 of the base of the sub- cylindrical stalk. 



2. The callosities consist, as seen in cross-section, of 20-30 

 vertical rows of cells, each cell containing abundance of reserve 

 material in the form of starch grains and crystalloids. 



3. The stalk has exactly the same structure as a callosity. Its 

 cells are, however, without reserve products. 



4. There is everything to indicate that the callosities are organs 

 of vegetative propagation, comparable in function to the gemmae 



1 T. Johnson : Journ. Linn. Soc, Bot. xxvii, 1891, p. 463. The systematic posi- 

 tion of the Dictyotacese, with especial reference to Dictyopteris, Lamx. 



