THE PRINCIPLES OF OAK GALL FORMATION. 7 



exterior, consisting of epidermis with iinicellnlar hairs 

 containing red pigment in their cell contents ; (2) 

 coloiirless hypodermal cells, beneath which is (3) a 

 layer of small meristematic cells ; then (4) a thick 

 layer of large cells rich in tannin, below which follow, 

 (5) the cambian ring, (6) primary starch cells, (7) cells 

 containing crystals, and (8) a thin layer of primary 

 nutritive tissue composing the walls of the larval 

 cell. 



The colours in many oak galls are very varied and 

 rich. 



They range from Avhite and cream through all 

 tints of yellow, from very pale to deep orange, and 

 from a very pale green to a rich dark hue, and through 

 almost every shade of red, some of the tints of which 

 are very attractive. Only one kind of gall yields a 

 purple, and that colour is in the hairlets with which it 

 is clothed {Spathegastev Taschenbergi). The browns 

 vary from very pale, through various shades of reddish- 

 browm, to chocolate. 



No English gall student appears to have published 

 results of investigations into the origin of the colours. 

 This is rather remarkal^le, because the colours are 

 always so prominently before the collector, and in 

 many instances it is the colour which gives the charm 

 to the gall. 



Dr. Marion Newbigin's researches (' Colour in 

 Nature,' 1898) have shed much light upon the 

 phj^siology of pigments and colours in plants and 

 animals. But the colours of vegetable galls do not 

 appear to have received her attention. Since most 

 galls are almost as complex in their structure as the 

 plant on which they grow, and as it has already been 

 shown, are so indissolubly associated with the ener- 

 gising functions of the tree, and also built up of the 

 same materials, may it not be inferred that the 

 coloration of galls is produced in the same manner 

 as in other parts of the plant ? 



Chlorophyll-green is, of course, the supremely im- 



