

f 



1917] CURRENT LITERATURE 157 



"(1) both an alternate and an opposite arrangement of bordered pits in the 



radial walls of the tracheids; (2) an unequal thickening of the walls and 



% lumina of the tracheids; (3) very short tracheids with blunt end walls, which 



resemble parenchyma cells except in the pitting; (4) cells which are transi- 

 tional between tracheids and parenchyma cells in the pitting; (5) the presence 

 of true wood parenchyma cells; (6) a small production of thin- walled summer 

 tracheids; (7) a probable absence of bars of Sanio from many of the tracheids; 

 (8) an increase in the number of rays in the gall wood; (9) a tendency toward 

 the production of multiseriate rays; (10) ray tracheids which are transitional 

 between those of hard and soft pines; (11) the presence of a balled or whorled 

 arrangement of tracheids in the tangential sections; (12) a great increase in the 

 number of resin canals in the gall wood, but no such increase in the uninfected 

 wood close by. The examination of this gall has revealed so many points of 

 anatomical interest that a further study of this subject seems to be worth 

 while. On this account the author expects from time to time to issue other 

 papers on the anatomy of Peridermium galls on pines and other conifers." 

 It remains for someone to make a study of the very early stages of this and 

 many other abnormal plant growths. 



Rosen 9 has made a study of the histology of the grape leaf gall. The 

 author has made a study of this gall from its very earliest stages to its maturity. 

 He summarizes his results as follows: "(1) the Phylloxera vastatrix leaf gall 

 P starts to develop on embryonic bud leaves; in 24 hours the insect produces 



I a depression at the periphery of which hairs are formed on the upper surface of 



the leaf; the depression is due to a lessened growth of the attacked mesophyll; 

 (2) after 3-4 days of insect attack the lower half of the leaf tissue which sur- 

 rounds the portion in which the proboscis is inserted has proliferated enor- 

 mously; the whole thickness of the leaf in the region immediately around the 

 proboscis shows no proliferation; that portion of the leaf which is beneath the 

 insect does not proliferate, but the upper half at the sides of the insect grows 

 and forms the walls of a large insect cavity; upper epidermal cells and several 

 layers of mesophyll cells in the portion of the gall below the insect show peculiar 

 thickening and dissolution of their cell walls; (3) gall development depends 

 upon leaf development; when the leaf reaches its maximum size, after 12-15 

 days of development, the gall becomes mature; (4) a mature gall shows but 

 j slight cuticular development and very few stomata; the mesophyll is a huge 



mass of compact, thin-walled, partly empty cells, some of which are under- 

 sized, and others enormously elongated; the vascular elements are scattered 

 by wedges of parenchyma cells; many unicellular and multicellular hairs grow 

 out from the gall; (5) chemical work on this gall shows it to be a structure in 

 which anabolic processes are lacking, and in which large amounts of simple 

 sugars and simple proteins are present; (6) the development of this gall does 



9 Rosen, Harry R., The development of the Phylloxera vastatrix leaf gall. Amer. 

 Jour. Bot. 7:337-360. 1916. 



