534 



We find further investigations of frost blisters in a work by Xoack'. who 

 comes to the conclusion that they are produced "because water from the 

 cells is pressed into the intercellular spaces and there turns to ice so soon 

 as the temperature falls to a certain degree below the freezing point, differ- 

 ing for the different varieties of plants." The formation of ice crystals 

 was found by Noack to be strongest at the place where later the separation 

 of the epidermis becomes visible. We owe a recent study to Solereder-'. 

 He observed in the leaves of Buxus the same hairy outgrowth of the meso- 

 phyll cell rows that I had found in apples, cherries, apricots and have illus- 

 trated in Pig. 107. Solereder has proved experimentally that this elongation 

 of the cells of the leaf flesh is a secondary phenomenon occurring with an 

 abundant supply of water. He removed the under side of the leaf and set 

 the plants in a moist place. Cuticular warts were then produced on the cell 

 membranes, similar to those which we have illustrated by the woolly stripes 

 in ai)i)le cores (p. 324) and lia\e ()bser\cd also in the frost blisters of cherry 

 leaves. The beginning of this hair-like elongation of the cells is found in 

 the sheath of the vascular bundles, i. e., in places where the cork disease of 

 the cactus (p. 429, Fig. 71) may be recognized as the initial point of the 

 diseased processes of elongation. We find in this an experimental proof of 

 our theory that the disturbances named may be traced back to excess of 

 moisture. 



We will discuss later, in connection with other mechanical disturbances 

 due to frost, the (|uestion whether the frost blisters were produced by the 

 crystallized ice, or formed previously by a difference in tension due to the 

 cold, thus oft'cring for the formation of ice the most convenient places of 

 deposit. We will for the present only emphasize the fact that the holes in 

 the tissue pictured in the apple leaf (on the upper side of the veins and 

 below on their scarps) are a typical frost peculiarity found frequently in 

 very difl'erent leaves which also remain green during- the winter. 



COMR-I.TKE Sl'I.lTTIN(; OF THK LkAVES. 



In some years with late frosts the phenomenon, in which the otherwise 

 continuous surfaces of tree leaves often appear slit and thereby approach 

 those forms which are characterized as "folia laciiiiafa" may be found not 

 infrequently. While, however, in commercial \arieties, the slit leaf form 

 is a condition fixed in the developmental course of the individual and may 

 be transmitted by grafting, the slitting due to frost forms a transitory stage 

 which, even in the same summer, may return to the normal leaf form. 



I had opportunity in the spring of 1903 to observe the very frequent 

 occurrence of the phenomenon in Aescuhis Hippocastanum^. The structure 

 shown in Fig. loS was restricted to the lowermost leaves of the shoot, i. e.. 



1 Noack, Fr., t)ber Frostblasen iind ihre Ent.stehung. Z. f. Pflanzenkrankh. 

 1905. p. 29. 



2 Solereder, H., tJber Frostblasen und Fiostflecken an Bliittern. Centralbl. f. 

 Bakteriol. 2d Section, v. XII, 1904, No. 6-8. 



3 Sorauer, P., Kammartige Kastanienbliittei-, Z. f. Pflanzenkrankh. 1903, p. 214. 



