Lehman: Conidial Formation in Sphaeronema 157 



For part of the work, the fungus was grown on both cooked and 

 uncooked sweet potato tissue for periods varying from thirty-six 

 hours to six days. Material was then fixed in weak chromo- 

 acetic solution (Schaffner's formula), dehydrated, imbedded in 

 paraffin, sectioned 3 to 5 /x thick and stained either with Flem- 

 ming's triple stain or Haidenhain's iron-alum haematoxylon. 

 Mycelial mats grown on sterilized cornmeal as a substratum were 

 likewise fixed, sectioned, and stained. For the study of living 

 specimens, material grown on a substratum of 10 gr. wheat flour 

 and 40 c.c. of water was especially favorable because of the 

 unusually large size of the conidiophores. Very good differ- 

 entiation was obtained when living conidiophores were stained 

 for a few minutes in a one per cent, solution of safranin in fifty 

 per cent, alcohol. Many observations were also made on living 

 unstained material. The course of development of the two types 

 of sporophores was followed by observations on the fungus cul- 

 tured in Van Tieghem cells. 



The Conidiophore 



Short spore-bearing branches, termed by Halsted and Fair- 

 child (1) the primary sporophores, arise in great numbers from 

 both aerial and subsurface hyphae. These primary sporophores 

 are produced singly or in clusters of as many as six. When 

 formed in clusters, the younger sporophore arises in order from 

 a basal cell of the next older (Fig. 2). These structures are 

 typically somewhat fusiform and usually consist of a basal por- 

 tion of one to four short, more or less barrel-shaped cells with a 

 long, tapering terminal cell which gives rise to the hyaline conidia. 

 The primary sporophores vary in length, for the most part, from 

 70 to 100 /x and measure 4.5 to 6.5^ at the thickest place. The 

 terminal cell of the primary sporophore is herein designated the 

 conidiophore. The conidiophore commonly has a length equal to 

 or greater than one half the total length of the primary sporo- 

 phore and the tip is usually narrower by 1 to 1.5 /x than the 

 bulbous basal portion. 



