8o BOTANICAL GAZETTE [january 



extraordinary thickness of the septa characterizing this species. 

 Actinomyces XVII, however, while less striking, probably repre- 

 sents more nearly the usual condition prevailing in the second 

 category. The segment of the filament wall evacuated by 

 the contraction of each two successive spores undergoes no 

 change until fractured by the disruption of the chain of mature 

 spores. 



In the third category {Actinomyces IV, V, VI, VII, and XII) 

 the cross-walls first undergo a deep constriction, which by involv- 

 ing the ends of the young cylindrical spores gives to the latter an 

 elongated ellipsoidal shape (fig. joa-d). The constricted septum 

 now gradually loses its staining properties, and appears to become 

 slightly drawn out in a longitudinal direction (fig. joe). A prepara- 

 tion stained with Delafield's haematoxylin usually shows many old 

 spore chains in which the individual spores are thus connected by 

 hyaline isthmuses. Occasionally an isthmus may be found with a 

 remnant of the old deep staining septum still unchanged in its 

 center (figs. i6, joe). 



Beyond these three t3^es of sporulation another must at least 

 be provisionally recognized, in which septa are either absent from 

 the developing sporogenous hyphae, or are not demonstrated by the 

 use of ordinary stains. The protoplast appears to contract at 

 regular intervals, yielding a series of non-contiguous spores, held 

 together for a time by the connecting segments of evacuated fila- 

 ment wall (fig. 73). It is this type of sporulation which Neukirch 

 and his followers, in opposition to Lachner-Sandoval, believed to 

 prevail throughout the genus. Neukirch's conclusion that septa 

 are never involved in the sporogenesis of Actinofnyces certainly 

 cannot be extended to the large majority of species ; and its applica- 

 tion to any forms whatsoever is associated with some reasonable 

 • doubt. The writer is inclined to believe that cross-walls appear 

 in the development of the sporogenous hyphae probably throughout 

 the genus, but in some members are too thin to be recognized as 

 distinct septa. Such an interpretation is suggested by the wide 

 range in the thickness of septa found to occur, from the very mas- 

 sive structures of Actinomyces II, through those of moderate thick- 

 ness in Actinomyces I, XII, and XVI, to the condition prevailing in 



