465 



only one tear or was not injured. The epidermis was not torn, but only the 

 walls and contents were browned. 



The heads were broken in a very charac- 

 teristic way. Fig. 92 shows a slight breaking, 

 with the axis making an obtuse angle (h). In 

 the more severely injured heads, the axis was 

 bent two or three times, and where bent was 

 almost bare. 



Fig. 93 shows the construction of the axis 

 where bent : g, ducts ; 2, torn parenchyma ; i', 

 a vascular bundle, which has been killed. 

 Laterally from this, at br, the tissue as a whole 

 was a deep brown. Where other heads had 

 been hit the epidermis was torn open ; the 

 bordering tissue had collapsed, fallen to pieces 

 and turned brown. Some vascular bundles 

 were found to be almost entirely isolated, since 

 the torn or disintegrated parenchyma had 

 cracked ofT. This might be a result of ten- 

 sion, since later the still green heads continued 

 their growth. The injuries vary very greatly 

 according to the way the hailstones strike. 

 Kraus's observation shows that after the hail- 

 stone had struck the head before it had become 

 rid of the leaf sheath, the beards remained 

 where they were. Therefore, the head ap- 

 peared bent like a bow. The injuries usually 

 were at the points where the young heads are 

 attached rather than in the internodes of the 

 axes. 



Oats will endure severe injuries if the 

 panicles are still enclosed in the upper leaf 

 sheath when the hail storm strikes them. Per- 

 fectly sterile heads may be produced and the 

 injury to the plants resembles that of thrip so 

 much as to lead to confusion. In some years 

 I have often found twisted barley heads due 

 to the sucking of thrip. PuppeU has often 

 studied the effect of mechanical blows and his 

 illustrations are very helpful. For example, 

 with a heavy smooth roller, he flattened a field 

 of young winter rye which had not yet formed 

 a blade. When the heads began to develop, 

 they were deformed exactly as if they had been injured by hail. 



1 Puppel, Max, Hagel- und Insektenschadeu. 40 plates from original photogr 



Fig. 92. Head of wheat broken 



by hail. The grains have fallen 



at the broken place, leaving it 



bare. (Orig.) 



iphs. 



