18 Mr Burdon, The Pine-apple Gall of the Spruce : 



her, renders her position most conspicuous. She undergoes three 

 ecdyses before reaching maturity, and the cast skins may be found 

 lying beside her in the " wool." As soon as she reaches maturity 

 she commences to lay eggs, and continues the process through 

 May and on into June, until a heap of some hundreds of eggs 

 accumulates beside her. Each egg is attached to the stem by a 

 delicate hair-like stalk. The first eggs begin to hatch soon after 

 the gall has emerged from the bud-scales, and the minute larvae 

 at once creep up the shoot and establish themselves in the 

 gall-chambers, where they find a fleshy succulent tissue already 

 prepared for them. They at once commence sucking and become 

 entirely enclosed within the chambers by the development of the 

 tumid lips previously referred to, and here they remain until the 

 galls open. 



These then constitute the most important events which 

 characterise the development of the galls during the first stage 

 — that is whilst still enclosed in the bud-scales. 



One very noticeable feature is the apparent absence of any 

 effort on the part of the plant to resist the attack, for the insect 

 appears to have everything its own way. This is I think chiefly 

 due to the fact that the shoot is enclosed in the bud-scales, which 

 exclude light and air, and thus keep the tissues of the shoot 

 in a plastic condition. Next season I hope to carry on some 

 etiolation experiments which will probably throw considerable 

 light on this point. It is of course also due in part to the 

 insect having, as it were, stolen a march on the plant, forcing 

 the young shoot to develope before it was fully prepared. 



Although my examination of the later stages is not yet 

 complete I have seen enough to convince me that the conditions 

 are reversed in the next stage, and a great effort is made by the 

 shoot to overcome the influence of the insect. And this effort is 

 to some extent successful in so far as the shoot is enabled to limit 

 the insect's sphere of influence to the area over which it has 

 already gained sway. But the effort is made too late, and always 

 ends in the death of the galled portion of the shoot, if not of the 

 whole shoot. 



With regard to the ultimate cause of the gall-formation there 

 is, I think, good reason to believe that it is due to an injection by 

 the Ghermes mother. It would be out of place in this paper to 

 give the reasons for this belief in detail, but the behaviour of the 

 chlorophyll, tannin, protoplasm and nuclei, and the gradual radia- 

 tion of the influence in every direction all seem to point to an 

 injection as the cause. Further, if the insect be removed, say a 

 week after it has commenced to suck, the abnormal growth is not 

 brought to an end. The gall continues to develope, and emerges 

 from the bud-scales just as if the insect had never been removed. 



