538 



also find the snow mold, the breaker of the rye blade, the killer of the wheat 

 blade, etc., all of which cause the further destruction of the plant. Besides 

 the browning of the vascular bundles in the plant nodes, the frost injuries, 

 predisposing the plant to fungous diseases, consist especially of a blister-like 

 raising of the outer membrane in definite places of the grain leaf. Such 

 blisters are found even in very young leaves in the bud as is shown in the 

 adjoining Fig. 109. We find that the outermost edge (B) of the young leaf 

 is so injured by frost that the cell contents have become brown and rounded, 

 the cells have collapsed and, therefore, die in a short time (gs). On the 



Fiff. ]09. Young- rye leaf, injured by fro.st. with eruplion.s nn the epidermis. 



other hand, the part of the leaf spirally rolled up (//) apjicars perfectly 

 fresh and capable of further development. 



The leaf, of which the outer side, while in the bud, is curved outward 

 like a bow, possesses a main vascular bundle (g) above which are deposited 

 hard bast cords (b) on the outside, and also weaker bundles (g'), ramifying 

 in the middle, broader region of the leaf, which nourish the increased meso- 

 phyll. Among the changes in tissue produced by frost, the one should be 

 emphasized in which the enlarged cells (r) become noticeable after the 

 thawing. These are radially elongated and in part irregularly pulled out of 

 shape (r), with greatly bowed walls. This condition proves the presence 



