X912] Morphology and Biology of Insect Galls 323 



There is a cambium layer lying just outside the protective zone in 

 the later stages. The nutritive layer consists of a mass of collapsed cells 

 that stain deeply with haematoxylin. These layers are shown in Fig. 37. 

 Lasioptera corni Felt. 



Cornus alterni folia L. 



' Cornus paniculata L'Her. 

 This gall appears on the upper side of the leaf as a circular elevation 

 but does not project on the under side. 



The colour is entirely green when young but becomes surrounded by 

 a circle of red at later stages. 



In anatomical structure the tissues that compose this gall are the 

 same as those in the normal leaf. 



The lower epidermis and the row of mesophyll cells immediately 

 in contact with it remain in the normal position. The upper epidermis 

 and the remainder of the mesophyll become arched and thus separate 

 from the lower epidermis and the part of the mesophyll that adheres to 

 it in the manner shown in Fig. 40. In the space thus formed the larvae 

 are found. 



Lasioptera impatientifolia Felt. 

 „ ( Impatiens hiflora Walt. 

 [Impatiens pallida Nutt. 



A monothalamous gall, projecting chiefly from the under side of the 

 leaf. It consists of an elongated, spindle-shaped swelling of the midrib. 

 Dimensions: — Longer diameter 8-12 mm. 

 Shorter diameter 3-4.5 mm. 

 Practically all the abnormal tissue in this case is produced from the 

 cortex of the midrib of the leaf. The stimulation has extended out only 

 a very short distance into the adjoining mesophyll. The general mass 

 of gall tissue consists of large cells with a few small intercellular air 

 spaces. The epidermal cells are larger than those of the normal epi- 

 dermis, their increased length being particularly noticeable. The features 

 are shown in Fig. 41. 



A nutritive layer is not differentiated. 



Neolasioptera perfoliata Felt. 

 Host Eupatorium perfoliatum L. 



A spindle-shaped swelling of the stem forming a monothalamous 

 gall. It varies in size in proportion to the diameter of the stem or branch 

 from which it originates. 



It may be stated as an almost invariable rule, that when a gall and 

 the plant organ from which it originates have a common epidermis the 

 cell walls of that epidermis are thicker in the area covering the gall than 



