544 



spilidlc is naked ln'twcfii the tip and the ha^e. In more extreme cases 

 of injury, in place ot' the head. onl\- a i'are, hrowii niemhraned spindle 

 with salmon-colored spots remains. The salmon-colored points are the 

 places of attachment of the i^rains and colored hy luxuriantly de\elopcd 

 tufts of fungi. 



In almost all cases of sterile-head condition, the axis is bent in the 

 form of a crook (F'ig. 1 14 I'> i' ) hy the drying of the bare part of the spindle. 

 In the examples pictured, it is clearly seen that the sterile head condition 

 owes its production to locally effective causes. When these phenomena 

 were studied on a field where especially many i)lHnts had suffered from 

 sterile-head condition, it was noticed that the zone of injury could be found 

 at approximately equal distances from the soil. Therefore, the injurious 

 cause must be found in a layer of air which is present exclusively at a 

 certain distance abo\ e the sf)il. The rye plants, aff'ected in different stages 



Fig. 115. 



Cioss-.sectiun IhrouKh the intc-inodo ol the head of a rye 

 Irom .sterility. 



ide sulLeriiig 



of indi\i(lual dexelopmcnt. are injured differentl}', according to the extent 

 to which they ha\ c penetrated into this injurious air layer. 



It is thus e\ ident that sometimes the lower part of the head w ill Itecome 

 bare, sometimes the ui)per part. In the best developed, tallest plants, in 

 which the heads, standing on the longest stalks, are already abo\e the 

 injurious air layer, the heads remain perfectly uninjured; onl)- the upper- 

 most section of the stalk has a pale band. 



In discussing the cause of this sterile-head condition, the sui)position 

 would seem most i)ertinent, that the disease is caused by the fungus, recog- 

 nizable on the l)and and especially on the spindle of the head and appearing 

 in salmon-colored ridges at the places of attachment of the blossoms. 



This hypothesis, however, is erroneous since even greater injuries to 

 the spindle hax'c been obser\ed when the presence of the fungus could not 

 be proved. On this account, this fungus, which belongs to the genus Acre- 



