340 Journal of Agricultural Research voi. vi. no. io 



held at room temperature, conidiophores and conidia appeared in lo to 

 12 days, which indicates that 5. atrovirens is one of the slow-growing 

 fungi. 



The conidia are formed first either at the apex or the distal end of the 

 intermediate cells. Under certain apparently abnormal conditions, 

 however, they appear at the ends of what seem to be ordinary branches 

 of the mycelium, but in that case the character of the normal conidio- 

 phore is absent. The lowest whorls of conidia are borne about halfway 

 between the base and the apex of the conidiophores, and the conidia are 

 attached at the broad end (PI. XLVI, fig. 2). 



Germination of the conidia takes place by means of germ tubes. These 

 are produced from either pole, generally from the distal or pointed end, 

 as well as from any cell of the conidium, as observed by previous investi- 

 gators. Germination in water occurs within 24 to 40 hours; and in a 

 few days the somewhat hyalin, knoblike protrusion, which is character- 

 istic of the early stages of germ formation, develops a multiseptate, 

 branched mycelium which is of a much lighter color than the conidio- 

 phores, conidia, or portions of the old mycelium. This is very hyalin 

 and continues so up to the time of conidiophore formation, at which 

 time dark-brown, thickened cells are formed in different parts, and from 

 these specialized cells are produced the many-septate, dark-brown coni- 

 diophores, which attain a length of 5 mm. and are perceptibly wider 

 than the surrounding mycelium (PI. XLVI, fig. i). 



Because of the wide variation found in the size of the spores, Appel and 

 Clinton (4, p. 359) suggested the possibility of there being two species 

 of the fungus — that is, a large-spore and a small-spore species. Several 

 series of 18 measurements were made by the writer on conidia taken from 

 tubers imported from Germany and tubers from various parts of the 

 United States. A wide variation in dimensions occurred in the conidia 

 from all the various tubers used in the experiment. The conidia taken 

 direct from the surface of the tuber from Germany varied from 22 to 42/i 

 (mostly 30 to 40) in length, 6 to 12/i (mostly 6 to 8) in width at greatest 

 diameter, and were 4 to 8 (mostly 5 to 6) septate; conidia taken from the 

 progeny of tubers from Maine grown in Washington, D. C, varied from 

 30.4 to 56.2^1 (mostly 30 to 40) in length, 7.6 to 9.5JU (mostly 7.6 to 8.5) 

 in width, and were from 4 to 7 septate; while the conidia taken from tubers 

 from Rhode Island, West Virginia, Washington, D. C, Oregon, Wash- 

 ington, and Wisconsin averaged 32.6 to 40// in length, 7.5 to 8.5jU in 

 width, and were 5- to 7-septate. 



In order to study more fully the variation of spore dimensions, several 

 series of measurements were made on conidia produced from a single 

 spore strain. ♦ The difference in dimensions obtained in this case ranged 

 from 18 to 64/i (mostly 30,4 to 40) in length, and 7 to S.i/x in width, 

 and 5 to 6 septa. 



