43-' 



which will later be described as intumescences. The causes will also be 

 taken up more in detail then. 



Jn the production of the perforations, individual nutrition plays a 

 ]jrominent part ; for. in the same place of growth, specimens which seem 

 almost eaten up. ma\- be found near plants which remain untouched. At 

 times, only isolated species suffer. Thus, for example, I found in groups 

 of different species of maple only one single vigorously growing variety 

 which was diseased, among other kinds (leveloi)ing normally. 



I'"oKMATIO\ OK (/ORK OX FrUITS. 



The brown, dull, not infrecjuently scaley spots or lines on the smooth 

 outer surface of apj)les and pears, the so-called rusty tracery is well-known. 

 Some \arieties show the phenomenon every year, so that it has been in- 

 cluded in the general description of the species. They are formations of 



cork, which, as a rule, arise from the 

 stomata. In some years the process be- 

 comes abnormal in its appearance, so that 

 not only "the \arieties with rust spots" 

 have a i)artial or entire cork-colored sur- 

 face, but also the fruits of varieties 

 usual ]>■ remaining smooth-skinned are 

 affected. 



Injuries to the epidermis when the 

 fruit first swells are the cause of this phe- 

 nomenon. In cases already known to me 

 (apples, pears, plums, grapes), it could 

 be proved that a light late frost had split 

 the cuticle covering of the young fruit in 

 innumeral)le small tears. Under these 

 microscopically small splits, the fruit at once formed cork layers. 

 In places the epidermal cells die and remain together with the first formed 

 cork layers as scales on the rather didl, leather colored surface of the fruit. 

 Whenever the corked places form a contiguous surface, the fruit in 

 development does not swell uniformly, with the result that huge spUts show- 

 on the fruit itself. The spores of Monilia especially enter these places and 

 mummify the fruit. 



But these phenomena, in the strictest sense, do not belong here They 

 are connected with an excess of moisture only in so far as the splitting 

 occurs the more easily, the more quickly the swelling of the fruit takes 

 place with continued moisture. 



On the other hand, I would like to consider the appearance of cork warts 

 on the stems of grapes as a process which becomes noticeable only in moist 

 air. In Fig. y^ we see two grapes, the stems of which exhibit a browned rough 

 surface due to the appearance of many cork-colored, closely distributed wans. 

 The phenomenon occurs before the grapes have reached their normal size. 



Fis. 73. Grapes with cork warti 

 (W) on the fruit stem. 



J 



