MONSTROSITIES AND MALFORMATIONS. 253 



climbers, wire, etc., have been described, and 

 fruits e.g. Gourds are easily distorted by means 

 of string tied round them when young. 



Distortions of leaves are very common, and are 

 sometimes teratological i.e. due to no known 

 cause e.g. the pitcher-like or hood-like cucullate 

 leaves of the Lime, Cabbage, Pelargonhnn, etc., 

 and of fused pairs in Crassula. Also coherent, 

 bifurcate, crested, displaced and twisted leaves 

 occasionally met with, and in some cases fixed by 

 cultivation, may be placed in this category. 



Puckers must be distinguished from pustules, 

 since they consist in local upraisings of the whole 

 tissue, not swellings e.g. the j^ellowish green 

 pockets on Walnut leaves, due to Phyllereuui. 



Puckered leaves in which the area of mesophyll 

 between the venation is increased by rising up 

 in an arched or dome-like manner are sometimes 

 brought about by excessive moisture in a confined 

 space. 



Leaf-curl is a similar deformation caused by 

 funsi, such as Exoascus on Peaches. 



Wrinkling or puckering of leaves is also a 

 common symptom of the work of Aphides e.g. 

 Hops. 



Characteristic curling and puckering, with 

 yellow and orange tints, of the terminal leaves of 

 Apples, Pears, etc., are due to insects of the genera 

 Aphis, Psylla, etc. 



Small red and yellow spots with puckerings 

 and curlings of the young leaves of Pears, the 

 spots turning darker later on, are due to Phytoptiis. 



