PINACEiE 309 



partly developed leaves and lays its eggs in them, thus causing the 

 leaf-bases to swell, enclosing the eggs, and later the larvae, and 

 producing small, pineapple-like galls. The only known means of 

 coping with this disease on a wide scale is to fumigate all stock 

 before removing it from the nursery. Decorative trees may be 

 sprayed with paraffin emulsion once every 8-10 days over a period 

 of weeks from the time when growth begins in spring. Another 

 pest is the spruce aphis {Aj^his abietina), a small green fly, which 

 causes the leaves to fall prematurely and eventually kills the 

 plants. Regular spraying with paraffin emulsion is the only 

 known means of checking this disease. Nursery stock should 

 be fumigated with hydrocyanic gas before distribution. It is 

 desirable that a sharp watch should be kept for this insect, as 

 it is spreading rapidly in some parts of the country and doing 

 much harm in plantations of Sitka spruce, not only amongst 

 newly planted trees but in well-established plantations. 



Note. — Great confusion has arisen owing to the different 

 senses in which the names Picea and Abies have been used by 

 different writers. By modern botanists the genus Abies is now 

 made to include all the silver firs and Picea the spruces. In 

 many nurseries and gardens, however, the arrangement proposed 

 by Loudon and Gordon, of including spruces under Abies and 

 the silver firs under Picea, is still followed ; such an arrangement 

 should be discontinued. 



In the fiat-leaved spruces, in which the stomatic surface is 

 morphologically the upper one, the twisting of the leaves on their 

 bases on the horizontal shoots in order to direct their upper 

 surfaces downwards differs from the arrangement in Abies, Tsuga 

 and Pseudotsuga, where the stomatic leaf surface is morpho- 

 logically the under one. 



Key to Picea. 



Leaves flattened, stomatic lines on one surface only. 

 Young shoots without hairs. 



Leaves on lower side of shoot arranged in two lateral 

 sets, exposing the shoot below. 

 Young shoots buff-coloured, becoming darker in second 

 year ; leaves bright green, silvery white beneath ; 

 slightly keeled on both surfaces. — P. brachylyla. 

 Young shoots pale buff, becoming red in second year. 

 Leaves dark green, silvery white beneath, shghtly 

 keeled on both surfaces. — P. jezoensis. 

 Young shoots yellowish, showing darker in second 

 year, deeply keeled on ventral surface, almost 

 convex on dorsal white surface, needle-like, very 

 prickly. — P. sitchensis. 



