r 





128 MISSOURI BOTANICAL GARDEN. 



ner in which the sprays were placed upon the leaf. Where 

 the spray was strictly in the form of small drops, the 

 distinct warts, as shown on plates 25 and 26, were always 

 formed. "Where the individual drops ran together inakino- 



$ blotches of the spray, either the entire 

 leaf became oedematous, or there were areas from one- 

 fourth to one-half inch square swelled out, forming enormous 



more or less larg 



massses of giant cells, as shown in plate 31. It will be 





noted that not 



only is the leaf lamina affected, but the 

 tissue immediately surrounding and composing the veins of 

 the leaf has likewise been affected. In this case, lon°- 

 lines of oedematous tissue formed on both sides of a vein, 

 breaking out much as in the case of the more circum- 

 scribed areas described above. 



The formation of the intumescences or oedemas has been 

 known for a long time, both on the leafy and woody parts 

 of a large number of plants. Sorauer 28 designated by the 

 name " Intumescentia " all those structures which appear 

 as small wart-like eruptions on the surface of leaves, sen- 



* T to 



erally yellowish in color and which show a more or less 

 unusual stretching of cells. On leaves the swellings gen- 

 erally originate in the mesophyll cells and consist of 

 hypertrophied cells, having a very thin lining of protoplasm, 

 very thin cell walls, and much reduced chlorophyll grains, 

 if any. In the majority of cases a simple stretching of 

 certain cells takes place, but in other cases an actual divi- 

 sion and multiplication of cells. This is not confined to 

 tho mesophyll, but may also take place with the epidermal 

 cells, as described by Sorauer 33 , in the case of intumescences 

 formed on pinks. It will not be necessary to describe in 

 detail the various structural modifications which have been 

 described from time to time for various forms of intumes- 

 cences on all kinds of plants. The reader is referred to 

 the writings of Sorauer 26-35 ; Kiister 11 - 12 ; Prillieux 20 ; 

 Dale 3 ; Trotter 37 ; and Atkinson 1 . 





