366 GENERAL PLANT PATHOLOGY 



Etiolated plants afford interesting examples of hypertrophy, for 

 in the absence of light the internodes of the stems and the petioles 

 of the leaves become inordinately long. If this follows cell divisions, 

 then it is a hyperplastic phenomena, but where it is due to the abnormal 

 lengthening of existing cells, it is a simple case of hypertrophy. Kiister 

 found in the etiolated peduncles of Tulipa Gesneriana, that the cells 

 were from a third to a half longer than the normal ones. Longer cells 

 than usual are produced in plants grown experimentally in moist air. 



Hyperhydric tissues are abnormal and are formed by an excess of 

 water within the plant. They constitute a homogeneous group from 

 a causative (etiologic) point of view. As examples may be cited 

 the spongy white masses of cells which appear in the lenticels of the 

 twigs of alder, poplar, willow when such twigs are placed in water. 

 The individual cells of this porous tissue are chlorophylless, have a thin 

 layer of cytoplasm and a clear abundant cell sap. Such water lenticels 

 were compared by Schenck with typic aerenchyma found on numerous 

 water plants. Such lenticel excrescences arise from normal lenticels 

 by the enlargement of the phelloderm cells and in some cases the bark 

 cells lying under the lenticel hypertrophy. Von Tubeuf and Devaux 

 give extensive lists of the plants which produce hypertrophied lenticels.^ 



Bark excrescences form another kind of hypertrophied tissue. 

 They have been produced experimentally on the bark of the red currant, 

 Rihes aureum (Fig. 144). In such boss-like excrescences the paren- 

 chyma cells of the bark grow out into long sac-like cells of different 

 form and size by growth in a radial direction. Not only the cells of 

 the outermost bark layers take part, but all the elements down to the 

 wood take part in the abnormal growth and have become completely 

 or nearly colorless. The firm connection between bark cells is lost and 

 they are separated from each other by large intercellular spaces. 

 Sorauer kept cuttings of shoots of Ribes aureum several years old in a 

 vessel of water and in moist air. At the end of four weeks extensive 

 excrescences were formed. 



Intumescences are small pustules, which are formed only in limited 

 areas, and their formation follows the same processes of growth as in 

 the case of bark excrescences. They are known in the branches of 

 Acacia pendula, Eucalyptus rostratus, Lavatera trimestris and Malope 



^ KtJSTER, Dr. Ernst: Pathological Plant Anatomy, authorized translation by 

 Frances Dorrance, 1913: 74-75. 



