262 The Ohio Journal of Science [Vol. XVI, No. 7, 



The galls are commonly torn open by birds to obtain the soft 

 insects within, which spend the winter in the galls. One of 

 these nymphs is shown on the gall (PI. XIX, Fig. 3). 



It is not definitely known whether the imagoes from this 

 gall and those from the next, P. gemma, are identical. The 

 nymphs appear to be identical. The galls, however, are dis- 

 tinct, a difference, however, which may be referable to the 

 plant part affected rather than to any specific behavior on the 

 part of the insects respectively. This matter will be explained 

 after P. gemma has been described. 



This gall started in a similar manner to that of P. vesiculum, 

 by the larva inducing a cone of tissue to grow over it, burying 

 it in the superficial layer of the young stem. This minute cone 

 early becomes obliterated. 



A transverse section of the stem and its gall is shown in 

 PI. XIV, Fig. 4a. The influence of the insect in modifying the 

 growth and differentiation of the embryonic cortical tissue, has 

 extended nearly around the stem. The outer protective layer 

 is much heavier and better defined than the inner. Two 

 prominent elongate, thick plates of mechanical tissue extend 

 from the broken inner sclerenchyma zone, outward toward 

 the attenuate edges of the outer mechanical layer; a definite 

 adaption to insure rigidity. The soft interior tissue bounding 

 the larval chamber is made up of cambium-like parenchyma, 

 the cells being very regularly oriented in radial row^s. This 

 constitutes the nutritive layer (PI. XIV, Fig. 4c). 



Fig. 4b shows in detail a part taken at b. Fig. 4a. The outer- 

 most sclerenchyma elements are true sclerides and have numer- 

 ous crystal containing cells scattered among them. The cork 

 enveloping the gall is normal, except that the number of cell 

 layers is not as numerous as in the unaffected stem. The 

 epidermis and often the hypodermal layer with it, is found 

 broken and peeling off, w^hile that on the stem opposite the gall 

 is intact. 



A much magnified detail (Fig. 4d) has been made from the 

 region d in Fig. 4 a, PI. XIV, to show the origin of the tissue 

 which has formed the bulk of the gall. At this point of transi- 

 tion between the hyperplasia tissue and the normal, it is at once 

 seen that the phellogen layer has furnished the meristematic 

 tissue, which has been directed to such unusual development, 

 for the new tissue is strikingly shown to be intercalated between 



