244 Howe: Phycological studies 



traversed by a central canal, yet in some cases the lumen appears 

 entirely closed. Some apparently mature sporangia show no trace 

 of a septum or plug, but in such instances similar plugs can usually 

 be found in the rhachis of the sporangiophore and it is probable 

 that these may serve as common septa for two or more sporangia. 

 A basal septum or plug has not been attributed to the sporangium 

 of Halimeda, so far as we know ; in fact, its existence has been 

 ■expressly denied,* yet from analogy with Codiumf of the same 

 family, and perhaps we ma}' say from analogy with the known 

 sporangia of the Siphonales in general, its presence is what would 

 be expected. In the fertile specimen from Bermuda, which we 

 believe referable to Halimeda Tuna, the material is less well pre- 

 served and less mature and the plugs are more difficult to demon- 

 strate, yet we have observed in this also a few undoubted instances 

 of their presence. 



We regret that the opportunity for seeing the living zoospores 

 of Halimeda scabra was not followed out. The material preserved 

 with the aid of formaldehyde does not enable one to get a very 

 good conception of the form and size of the zoospores, but the 

 protoplast of the sporangium often shows a minutely polygono- 

 radial structure at its periphery. 



Siphonocladus rigidus sp. nov. 



Caespitose, subfastigiate, rigid, the cushions 2-5 cm. high, of 

 a light translucent green when living : primary ramification 

 mostly dichotomous or subdichotomous, the main axes often 

 also with irregular or subsecund, lateral prolifications : filaments 

 350-1 150// broad, consisting usually of a single series of cells, % 

 but often, especially under the dichotomies, becoming two or 

 three cells in width owing to longitudinal or oblique divisions : 

 cells variable in length, mostly about as long as broad, those of 



* Schmitz. Sitzungsber. d. niederrheinischerGes. f. Natur- und Heilkunde, 1879 : 

 143. 1880. — Wille ; Engler & Prantl, Nat. Pflanzenfam. i 8 : 140. 1S90. 



| Harvey-Gibson, R. J., & Auld, H. P. Codium. L. M. B. C. Memoirs, IV. 

 1900. 



I We are aware that certain modern biologists object to applying the word "cell" 

 to the segments of a coenocytic plant like Siphonocladus, but its use in this sense is 

 historically and etymologically more accurate than its proposed modern restriction to 

 the " energid " of certain physiologists. Moreover, no substitute entirely satisfactory 

 to the systematist has been suggested. Proposed equivalents, like "segment,'' " com- 

 partment," and " coenocyte " are often either ambiguous or unnecessarily awkward. 



