506 Howe : Phycological studies 



are anything other than normal parts of the Avrainvillea itself ; they 

 certainly contain chlorophyl and starch and the chloroplasts appear 

 to be of the same character as those of the ordinary filaments of 

 the thallus. Indeed, the supposed sporangia occur in too great 

 profusion, even though on a single plant, and they are too regular 

 in form and position, we believe, to be anything else than normal. 

 The sporangia are always terminal on branches, which, except 

 for the presence of the sporangium, are but slightly different from 

 the ordinary vegetative filaments of the flabellum, being, however, 

 less moniliform or torulose, and often more slender than the fila- 

 ment from which they spring. These sporangiophores result from 

 the ordinary forking of the filaments and they are commonly 

 homologous with a vegetative branch which would undergo two 

 or three more dichotomies (figure i 5). Some which can be traced 

 back to the deeper-lying filaments are falsely lateral in origin. The " 

 form of the sporangia has been alluded to above, but the figures 

 published herewith give a more accurate idea of their character. 

 They vary from 0.35 to 0.83 mm. in length and from 0.20 to 

 0.35 mm. in width. Sometimes, as shown in figures 22 to 24, the 

 base of the sporangium, underneath the spores, is occupied by a 

 brownish mass of slime or mucilage, forming a more or less com- 

 plete basal septum. The plug, however, is perhaps more com- 

 monly near the base of the sporangiophore, as shown in figure I 5. 

 Occasionally, as in figure 13, the stoppage is near the middle of 

 the sporangiophore. Often, two such plugs may be found, one at 

 the base of the sporangium and the other at the base of the spor- 

 angiophore. The brown callose-mucilage evidently furnishes the 

 material for healing the wound caused by the withering away of 

 the empty sporangium. Numerous brown, rounded, thick-walled, 

 stump-like processes, like that shown in figure 20, may be found, 

 indicating the position of former sporangiophores. It rarely hap- 

 pens that practically the whole protoplast of the sporangium is 

 consumed in the formation of a single spore, but the usual number 

 is three, four, or five, as stated above, though occasionally as many 

 as six, seven, or eight are formed. The spores are most commonly 

 long-ovoid or pyriform and as they lie in the sporangium the 

 broader end is usually upward. They are densely crowded with 

 chloroplasts and starch-grains but as they mature the amount of 



