1912] 



Morphology and Biology of Insect Galls 



3^9 



Mesophyll 



Resin Canals 



Endodermis 



Transfusion Tissue 

 of the Pericycle. 



Non-pitted Paren- 

 chyma of the Peri- 

 cycle 



Fibro-vascular 

 Bundle 



Usually two layers 

 of palisade paren- 

 chyma developed 

 on the upper leaf 

 surface. The re- 

 mainder of the me- 

 sophyll consists of 

 spongy parenchy- 

 ma (Fig. 28). 



Two circular canals 

 present. These con- 

 sist of an outer 

 layer of thick 

 walled cells and an 

 inner epithelial 

 layer of thin walled 

 cells. 



Consists of a single 

 layer of thin-walled 

 elliptical cells that 

 bound the me- 

 sophyll on the in- 

 side and separate it 

 from the pericycle 

 (Fig. 31)- 



Always present : 

 found in two 

 masses, one bor- 

 dering each phloem 

 area (Fig. 31). 



Fills between the 

 two divisions of the 

 bundle and projects 

 on each side but 

 more plentifully on 

 the dorsal (Fig. 

 31). 



Phloem and xylem 

 consist of an aver- 

 age of 7 rows of 

 cells. Medullary 

 rays found between 

 the rows. 



No distinction be- 

 tween palisade cells 

 and spongy par- 

 enchyma. 



Irregular; varying 

 in form and size, 

 on account of the 

 absence of the layer 

 o f strengthening 

 cells. 



Endodermis seldom 

 d istinguishable. 

 Cells irregular in 

 form and size. No 

 distinct boundary 

 between mesophyll 

 and pericycle. 



Nearly always 

 present. 



More irregular in 

 form and size. 

 Larger and thicker 

 walled than in nor- 

 mal. 



Phloem and xylem 

 less developed than 

 in normal. The 

 cells are often 

 larger and thicker 

 walled. Medullary 

 rays are absent. 



The same as the 

 preceding in the 

 fungus, but the cells 

 are very much 

 elongated in a plane 

 perpendicular to 

 the midrib and 

 parallel to the epi- 

 dermis. 



Resemble the nor- 

 mal cype in shape 

 and are the same in 

 number, but are 

 considerably larger 

 and the strength- 

 ening layer con- 

 sists of very irreg- 

 ularly shaped cells. 



Only a few cells 

 differentiated and 

 these are irregular 

 in shape and much 

 enlarged (Fig. 30). 



Found in from 2-4 

 layers around the 

 inner side of the 

 endodermis. It 

 comprises the great- 

 er part of the peri- 

 cycle. The cells 

 contain protoplas- 

 mic material (Fig. 

 30). 



Developed only be- 

 tween the bundles 

 and in a single row 

 along the edge of 

 the bast (Fig. 30) . 



Phloem and xylem 

 better developed 

 than in the normal, 

 the latter is more 

 irregular. The me- 

 dul'ary rays are 

 abseat. 



Cecidomyia impatientis O.S. 

 Host Impatiens hiflora Walt. 

 A spherical, polythalamous gall attached to the host plant by a 

 tapering stalk. Produced by the deformity of a flower bud. 

 Dimensions : — Diameter at right angles to stalk axis 6 mm. 



