The Take-all Disease of Cereals and Grasses 25 



which was known to be free from the organism. Twenty-one rod-rows 

 of winter wheat were planted with seed obtained by hand-threshing 

 diseased plants collected from all the infested fields surveyed in 1921. 

 Special care was taken in the threshing to see that no part of the culms 

 became mixed with the seed. No symptoms nor signs of take-all were 

 observed in any of these rows. In addition to this test, 77 rod-rows of 

 winter wheat were planted with seed that came from a badly diseased 

 field, the grain of which was threshed by the usual methods. One or 

 two diseased plants appeared at one place in these rows. This seemed to 

 indicate that the pathogene may be carried with seed in w T hich bits of 

 diseased culms have become mixed. 



It appears, however, that the ascospores constitute the inoculum for 

 the vast majority of infections. The perithecia in which they are devel- 

 oped are usually produced in great numbers on wheat, on barley, and 

 on many grasses. These minute dark brown to black, rostrate fruit 

 bodies (Plate II, C and D) are most commonly and abundantly developed 

 beneath the leaf sheaths of the lower internodes. They occur also on 

 the roots in the thick wefts of fine rootlets developed above the diseased 

 crown. They are gregarious or scattered. When young the perithecia 

 are hidden, but at maturity their prominent beaks protrude through the 

 leaf sheath. 



These perithecia contain numerous elongate clavate asci, each con- 

 taining eight spores (Plate 11, B). These ascospores are long, slender, 

 and hyaline, and are continuous when young but at maturity are 5-7- 

 septate. They measure 60 to 107 by 3 to 3.75 fx. They do not usually 

 become fully mature until early autumn. 9 



In the examination of several thousand individuals it has been noted 

 that soon after formation the perithecium contains a few apparently 

 mature and many immature ascospores, and that during the following 

 nine months it always contains a proportion of immature ascospores. 

 Hori (1901) states that in Japan the ascospores germinate in June and 

 July. McAlpine (1904) reports that in Australia they germinate during 

 November, and Robinson (1907) finds them capable of germinating immedi- 

 ately after formation if sufficient moisture and air are present. How- 

 ever, no investigator has reported on a careful study of their longevity. 



With a view of ascertaining the length of the period during which 

 ascospores will germinate, field material was collected and stored under 

 field conditions in 1920, 1921, and 1922. During those three years 

 attempts were made to germinate the ascospores nearly every month. 

 The results of these tests show that ascospores formed in June and July- 

 have in some years failed to germinate and have in other years germi- 

 nated to a small extent (less than 5 per cent) in July and August of the 



'A detailed description of the morphology of the perithecium has been given by Fitzpatrick, Thomas, 

 and Kirby (1922:36-37). 



