— 79 — 



some cases combined with transverse axial abscission (at.) B. Lateral axial ab- 

 scission in two adjacent nodes. C. Diagram to show the relation of transverse 

 and axial abscission layers. D. A lateral axial abscission layer which passed 

 through a leaf base. 



Fig. 4. Diagram of position of cut which may be made without causing 

 ?^JScission so long as the leaf does not wither. 



Fig-. 5- Two abscission layers beguming at a and b, and meeting at c, above 

 opposite leaves. 



Fig. 6. The confluence (c) of two abscission layers (a and b) when the 

 nodes were separated about 7 mm. 



Fig. 7. Diagram to show twisting of the abscission layer. 



Fig. 8. The course of the abscission layer in a peduncle. 



Fig. 9. The course of the abscission layer in a vegetative stem. This is the 

 usual course. 



Fig. 10. An abnormal case of the same. 



Fig. II. A young twig of willow in which abscission began but was inhibit- 

 ed, after which an oedema set in. 



SOME USEFUL KEYS TO SOME IMPORTANT ECONOMIC 



INSECTS 



By W. Lochhead, Macdonald College. 



COOCIDAE. 



The Chief Sub-Families and Genera. 



Chief Suh-Families. 



A. Abdominal spiracles present on each segment ; males with compound eyes ; 



adult females with white waxy lamellae — Orthezinae. 

 AA. Abdominal spiracles absent ; males with simples eyes ; 



B. Concealed beneath a "scale", formed partly of larval exuviae, partly 



of secretion; abdomen ending in a "pygidium" — Diaspinac. 

 BB. Naked or covered with a waxy secretion, but not beneath a "scale" ; 

 abdominal pygidium absent. 



C. Extremity of abdomen cleft; anal orifice closed above by a 

 pair of triangular plates, anal ring fringed with setae ; waxy 

 scale not separable from the insect — Coccinae. 

 CC. Extremity of abdomen not cleft ; no anal triangular plates, 

 anal ring without setae — Dactylopinae. 



Chief Genera of the Diaspinac. 



A. Scale of female circular to oval with central, sub-central, or sub-marginal 

 exuviae. 



B. Scale of male resembling scale of female in colour and texture ; only 

 slightly elongated. 

 C. Pygidium with 6 groups of circumgenital gland-orifices — Com- 



stockiella. 

 CC. Pygidium with less than 6 groups of gland orifices. 



