LIBRARY 

 NEW YORK 



JOURNAL 



uARDe/V 



OF THE 



ROYAL MICROSCOPICAL SOCIETY. 



AUGUST 1886. 



TRANSACTIONS OF THE SOCIETY. 



XI. — Notes on the Structure and Evolution of the Floridese. 

 By George Massee, F.R.M.S. 



(Bead UtJi April, 1886.) 

 Plates XII. and XIII. 



Notwithstanding the marked variety of form and structure met 

 with in the vegetative parts of Floridese, an examination of the 

 groups shows that there are but few types of structure, all of 

 which can be traced back to a primitive form, illustrated by such 

 genera as Chantransia Thur. (C. corymbifera Thur.) and Balbiania 



EXPLANATION OF PLATES XII. and XIII. 



Fig. 1. — Trentcpohlia virgatula Harv. Showing apical cells, a, d, e, also the 

 segment or daughter-cell just after segmentation, b,f. This figure also illustrates 

 the mode of branch formation by lateral protrusions from cells behind the apical 

 cell ; at c the first indication of a lateral branch is shown. The branches are 

 developed in acropetal order. X 300. 



Fig. 2. — Porphyra laciniata Ag. Showing numerous apical cells, a, a, a, a ; 

 6, segment yet entire and watchglass-shaped. x 300. 



Fig. 3. — Ahnfeldtia plicata Fries. Showing the origin of the multicellular 

 thallus to be due to peripheral or pericentral cells cut off from an axial cell ; a, 

 apical cell ; b, segment, x 300. 



Fig. 4. — Transverse section through fig. 3 at the point c, d ; axial cell a, 

 pericentral cells 6, connected by threads of protoplasm. Further back the thallus 

 becomes thicker owing to the segmentation of the pericentral cells by radial and 

 tangential septa, x 300. 



Fig. 5. — Halurus equisetifolius Kzg. Showing the apical cell a, surmounted 

 by the uppermost whorl of branches, b. x 300. 



Fig. 6. — Dasya coccinea Ag. Illustrating the formation of branches by 

 divisions of the apical cell ; the two cells a, a, are the basal cells of new branches. 

 If they develope equally, a dichotomy will result ; 6 is the terminal cell of the 

 podium from which the two branches a, a, origiuate. x 300. 



Fig. 7. — D, coccinea. Illustrating monopodial branching, resulting from 

 division of the apical cell. The cells a, a', correspond to a, a, in fig. 6, but a 

 continued developing in the same direction as the podium, of which 6 is the 

 uppermost cell, while the sister cell a' grew at an angle. The cells a, a', are each 

 connected by protoplasmic threads with three other cells. X 300. 



Figs. 8 & 9. — Ceramium rubrum Ag. Showing that the incurved tips of the 

 Scr. 2.— Vol. VI. 2 P 



