BY ALEX. G. HAMILTON. 789 



benefit these little animals may be to the plant, he says they eat, 

 and as a consequence excrete and give off gases, and he thinks 

 it probable that the excreta and gases are absorbed by the plants, 

 which are thus benefited. He also speculates as to whether 

 certain crevices observed in some fruits may not be domatia to 

 shelter the mites till the young plant grows and gives them the 

 leaf-domatia. Still another service they may do is that they may 

 eat the spores and m3'celia of noxious fungi which rest and 

 germinate on the leaf, and in support of this he mentions having 

 seen minute rings which were undoubtedly the chewed mycelia, 

 and also digested spores in the excreta. Some of the strongest 

 evidence he has to offer in favour of there being a relation of 

 mutual helpfulness Ijetween the two is as follows. 



Speaking of Psychotria (laphvoides he says : " I have kept a 

 specimen of this species for six years in a dwelling room. When 

 it was brought thither the domatia were for the most part 

 inhabited, l)ut afterwards the mites almost entirely disappeared, 

 partly because they were swept off with a brush, and partly 

 banished by smoking. It was curious to observe how the unin- 

 habited domatia on the new sprouts altered by degrees, the hair 

 formation almost entirely disappeared, the opening widened, and 

 the inside of the domatium passed into a shallow cup-shaped 

 depression .... On some leaves the domatia have almost 

 entirely disappeared, and the epidermis in the vein-axils has by 

 degrees assumed the same appearance usual to the under side of 

 the leaf. At the same time the domatia which remain inhabited 

 retain their normal form. From these facts, it may, in my opinion, 

 be inferred that when the corresponding organs on a sprout find 

 no opportunity for action, i.e., do not become inhabited, the 

 domatia on the following lateral sprouts become more and more 

 rudimentary till they disappear. Whence it follows that the 

 importance of the domatia depends on the little creatures inhabit- 

 ing them " (1, p. 15). 



Speaking of the protoplasm in the cuticle of the domatia walls : 

 " It remains to examine more closely how this protoplasm behaves 

 in cells which lie under the excrement of mites; in some sections 

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