1912] Morphology and Biology of Insect Galls 347 



tissue which pass inwards from the gall rind; this gives the species a 

 superficial resemblance to small specimens of Amphibolips inanis OS. 



Dimensions: — Diameter 10-15 mm. 



The larval chamber in this species is suspended at the centre of the 

 gall by fine strands of tissue. These are composed of long, narrow, fila- 

 ment-like cells interspersed with spiral vessels. These fibres represent 

 the inner part of the parenchyma zone. The outer part of this zone 

 resembles closely that found in the gall produced by Dryophanta palus- 

 tris O.S. The cell walls of the epidermis are strongly thickened and this 

 is the case also in the underlying layer of cells of the parenchyma sheath. 

 The protective zone, when the gall is full grown, consists of two rows of 

 porous, laminated sclerenchyma cells. The outside tangential walls of 

 these cells are much more thickened than the inside walls. The cells of 

 the nutritive layer are unusually large and almost square in outlme. By 

 the time the gall is nearly mature many of them have been emptied of 

 their contents and a wrinkling in the radial walls shows that the whole 

 tissue is collapsing (Fig. 59). 



Andricus piger Bassett. 

 Host Quercus coccinea Muench. 



A polythalamous gall produced by the swelling of the petiole or 

 midrib of the leaf. It is situated always near the distal end of the petiole 

 or the proximal end of the midrib. 



It is an irregular, elongated structure, somewhat triangular in cross 

 section. When it originates from the midrib the projection is almost 

 entirely from the under surface of the leaf, the broad flattened part of 

 the midrib above rising very little above the general surface of the blade. 

 On the under surface of the leaf along each side of the gall is a row of 

 small openings. The larval cells are in two rows following the line of the 

 openings. The total number in the gall varies from 20 to 30. 



Dimensions: — Length of longer diameter 20-25 mm. 



A nearly mature specimen shows the following anatomical character- 

 istics. The four typical zones are well defined. Surrounding the nutri- 

 tive zone are three rows of cells that form the protective zone. The walls 

 of these cells are porous laminated and uniformly thickened. Outside of 

 the protective sheath is a zone of tissue of about the same width, each 

 cell of which contains a large crystal aggregate. These masses of crystals 

 alone distinguish this tissue from that of the parenchyma zone into which 

 it gradually passes by the crystal groups becoming less plentiful. 



Connected with the openings mentioned in the macroscopic descrip- 

 tion are remarkably straight canals that extend in as far as the protective 

 sheath. At this point they are closed by cone-shaped plugs of scleren- 

 chyma (Figs. 43, 44), that extend out from the protective zones of the 



