340 BROOKLYN BOTANIC GARDEN MEMOIRS 



and Pole Evans^ in his careful investigation of the histology of nine 

 species of cereal rusts has shown that while the young haustoria of 

 various species may be small and sac-like, or even "hammer-headed" 

 in others, the prevailing type of mature haustoria in these cereal rusts 

 seems to be the cylindrical or branched form. 



Attention was called in the earlier description of Botryorhiza to 

 the fact that Lutman had figured botryose haustoria in Doassantia 

 and it was there suggested that this Porto Rican rust might have some 

 other features in common with smuts. But the fact that the sporifer- 

 ous hyphae are sent out through a stoma or through the ruptured 

 epidermis before the spores themselves are cut off from their tips, and, 

 further, that there is produced in Botryorhiza (and apparently in rusts 

 in general) a definite, superficial hymenial layer from which the spores 

 arise constitutes two essential points of difference from the smuts. 

 The latter, as Lutman has clearly emphasized,^ have their spores pro- 

 duced either from a group of deeply imbedded multinucleate hyphae, 

 which break up directly into spores (in the Ustilaginaceae) or from 

 the tips of the side or main branches of the prevailingly binucleate 

 hyphae (as in the Tilletiaceae). 



It has also been brought out in the description of the characteristics 

 of Botryorhiza that the mycelium is composed of a branching system 

 of very coarse hyphal threads. These hyphae measure from 5 to 7 ju 

 in diameter. In my own work on various rusts, I had never before 

 met with such a coarse mycelium. Pole Evans, ^ however, has called 

 attention to the fact that the mycelial threads of Puccinia glumarum 

 reach the relatively enormous size of 10 to 19^1 in diameter; also 

 Dodge in his paper in this Memoir^ has noted that Farlow^ and 

 Wornle^" have found the hyphae in Gymnosporangium Ellisii to be 

 exceptionally large, being, according to the latter author, about 8 n 

 in diameter. 



^ The cereal rusts. I. The development of their uredo mycelia. Annals of 

 Botany 21: 441-446. 1907. 



^ L. c, p. 1218. 



' L. c, p. 451. 



* See p. 128. 



^ The gymnosporangia of the United States. Ann. Mem. Boston Soc. Nat. 

 Hist. 1880: 1-38. 



^^ Anatomische Untersuchung der durch Gymnosporangium-Arten hervor- 

 gerufenen Missbildungen. Forst. Nat. Zeits. 3: 68-84; 129-172. 1894. 



