The Take-all Disease of Cereals and Grasses 27 



It is clear that the behavior of the ascospores at the time of their dis- 

 charge restricts the agents of dissemination almost completely to rain. 

 To determine whether they could live long enough to be wind-borne, 

 the following test was made. A suspension of ascospores and asci was 

 prepared, small drops of which were placed on cover slips and allowed to 

 dry. At definite time intervals after .the drops had dried, water was 

 again added and the cover slide was put over a Van Tiegem cell in an 

 attem pt to germinate the spores. The results were as follows: ascospores 

 in unexposed controls germinated 49 per cent; free ascospores exposed 

 for two minutes germinated 2 per cent; free ascospores exposed for 

 three, five, ten, and thirty minutes, and one, two, and twelve hours, 

 failed to germinate. Asci exposed for three minutes showed ascospores 

 germinating in 40 per cent; those exposed for five minutes showed 35 per 

 cent germination; those exposed for ten minutes showed 16.6 per cent 

 germination ; and those exposed for thirty minutes and for one, two, and 

 twelve hours failed to show any germinating ascospores. 



Hori (1901) states that spores are disseminated in the soil near the 

 host and that wind may carry them for a short distance. Results of 

 the present investigation indicate that ascospores, and to a certain extent 

 asci, are so susceptible to drying that they cannot be transported in this 

 manner. Besides the dissemination of single ascospores, the fungus may 

 be carried as perithecia on host tissue. Waters (1920 a) states that infected 

 fragments may be carried by animals, wind, and cultivating tools, and 

 McAlpine (1904) believes that much of the dissemination of the fungus 

 in parts of Australia is due to dust or wind-blown soil. Mycelium harbored 

 on the rootstocks of perennial grasses may be scattered by cultivation. 



Mangin (1899), Hori (1901), McAlpine (1904), and Waters (1920 a) 

 have all stated that the roots serve as the infection court and that they 

 were unable to get infection on the upper part of the wheat plants. The 

 results obtained during the present investigation corroborate their 

 findings. 



Incubation. — -In water cultures, ascospores germinate either when free 

 or while still in the ascus. Germination begins in about ten hours, by 

 the pushing-out of a germ tube from one or both ends and in some instances 

 at points near the middle of the ascospore. A knob-like swelling, of a 

 diameter of 5 to 8 ju, has been observed to develop at the end or along the 

 middle of the ascospore. One or more germ tubes emerge from the 

 distal end and the sides of this swelling. 



Sickle-shaped microconidia, which seem to be functionless, may bud 

 out from the ends and the sides of the ascospores. These microconidia 

 are hyaline, measuring 5.5 to 8 by 1.5 to 2 fi. They are borne also on 

 the ends of certain hyphae which function as conidiophores. Foex (1919 c) 

 considered them sporidia and tailed them falciformers. McAlpine (1904) 

 recorded their presence without giving any hint as to their function. 



