94. BOTANICAL GAZETTE [july 



(3) by hypertrophy, (4) by atrophy. This paper is well illustrated and leads 

 the thoughtful American botanist to realize the enormous amount of research 

 work that could be carried on in this country on this one branch of cecidology 

 or plant pathology. 



The recent American literature presents a paper by Parrott and Hodg- 

 kixs 12 in which the authors describe the pathological condition caused by the 

 false tarnished plant-bug (Lygus invitus). This pest attacks the fruits before 

 they are one-half inch in diameter, causing many of them to fall. The injury 

 is said to be quite characteristic. "As the pears grow, the outer layer of the 

 skin about these spots becomes ruptured, and a light-yellow, mealy-appearing 

 growth of the inner layers of skin protrudes, making more or less triangular, 

 granular spots; or when two or more spots run together a patch or crack lined 

 and bordered w T ith corky tissue. The yellowish, protruding growth at first 

 makes a marked contrast with the smooth green skin of the little pear; and 

 later the cessation of growth at these points causes depressions and marked 

 general deformity of the fruit. In the flesh beneath, also, hard, gritty granula- 

 tions are produced, through which it is difficult to cut with a knife. " This 

 paper illustrates another broad field of plant pathology and physiology which 

 is practically untouched by American botanists. 



One of the most satisfactory pieces of scientific cecidology of recent years 

 is Triggerson's 13 work on Dryophanta erinacei. The author begins his study 

 with the well known Acraspis erinacei or hedgehog-gall which occurs on the 

 white oak, and proves it to be caused by a dimorphic species of insect. The 

 insects from this gall are agamic and oviposit on the leaf and flow r er buds of the 

 same host, causing an entirely different gall giving rise to the sexual form which 

 belongs to the genus Dryophanta. The author also gives the results of some 

 very interesting studies of the parasites and inquilines, and finally some 

 studies leading to the conclusion that the stimulus is due to a fluid secreted by 

 the malpighian vessels of the larva. However, comparative studies indicate 

 that this is not necessarily true in the case of other galls. The physiological 

 side of this paper will be of great interest to those plant physiologists and 

 pathologists who can overcome their prejudice long enough to give it careful 

 consideration. 



Another exceptionally good piece of work which is strictly botanical is by 

 Stewart 14 and treats of the anatomy of the black knot (Plowrightia morbosa). 

 The author finds that these knots may originate from spore infection from 



"Parrott, P. J., and Hodgkins, H. E., A pear-deforming plant bug. New 

 York Agricultural Experiment Station (Geneva) Bull. 368. 1913. 



* Triggersox, C. J., A study of Dryophanta erinacei (Mayr) and its galls. Annals 

 Ent. Soc. America 7:1-34- pis. IX. 1914. 



** Stewart, Alban, The anatomy of other features of the black knot. Amer 

 Jour. Bot. 1:112-125. 1914. 



