284 The Phenomena of Morphogenesis 



Prosoplasmatic galls are so numerous and so remarkable in many re- 

 spects that they have received much attention and are the basis of an 

 extensive literature. They are discussed in many papers and books by 

 Beyerinck (1883), Molliard (1895), Magnus (1914), Thompson (1915), 

 Felt (1917), Kostoff and Kendall (1929), Kiister (1930, 1949), Ross 

 (1932), Carter (1939, 1952), and others. A typical example has been 

 described in detail by Hough ( 1953 ) . 



The small galls produced by some of the rusts or by Synchijtrium pilifi- 

 cum on the leaves of Potentilla may perhaps be included among proso- 

 plasmatic galls, as may those formed on the petioles of Populus by 

 Pemphigus bursarius. Here the gall is simply a mass of expanded epider- 

 mal and cortical cells which have divided anticlinally. 



Fig. 11-6. Insect galls on leaf of rose. (From Wells.) 



There is a higher degree of organization in cynipid galls, and they have 

 received much more attention than any others (Fig. 11-6). In these the 

 female wasp deposits an egg in the body of the plant, where the larva 

 develops, and the gall results from the reaction of plant tissues to stimula- 

 tion from the egg and the developing larva. Such galls possess a concen- 

 tric type of organization. The histology of these structures is as varied as 

 their form (Figs. 11-7, 11-8). Some are relatively simple but others con- 

 sist of three, four, or even five different types of tissue. Some of these 

 tissues show adaptation to specific functions such as mechanical support, 

 storage, and aeration. The mechanical tissues are of particular interest be- 

 cause of their relation to the position of the larva within the gall and the 

 means of its escape. 



The special morphogenetic significance of these galls is that in them a 



