7G0 DOMATIA IN CERTAIX AUSTRALIAN AND OTHER PLANTS, 



e.g., Euhiaceoi (famous also for an4>domatia) show a marked pre- 

 disposition to acarodomatia. Many groups seem entirely with- 

 out them, e.g., Monocotyledons and Gymnosperms, and all herbs. 

 They are most abundant and best developed in tropical (and 

 temperate) zones. 



"In the second chapter the author discusses in detail the 

 various interpretations which may be put upon domatia. (1) 

 They may be pathological, like galls; (2) they may be for catching 

 insects ; (3) they may have only an indirect connection with 

 their tenants; (4) thty maybe of use to the plant as the dwellings 

 of commensals. He adopts the last interj^retation. He draws 

 an interesting parallel, however, between galls and domatia, and 

 is inclined to suppose that the domatia were first directly caused 

 by the insects, but have gradually become inherent, transmitted 

 characteristics. The author gives a clear table, distinguishing 

 the cecidia or galls due to ' antagonistic sjmibiosis,' either plant 

 or animal, (jihyto- and zoo-cecidia), and domatia due to ' mutual 

 symbiosis,' either plant or animal (ph3-to- and zoo-domatia). Those 

 due to plants are again subdivided into myco- and jDhyco-cecidia 

 or -domatia." 



Mr. Cheeseman's remarks are very interesting, not only because 

 his paper was published in the same year (1887) as Lundstrom's,. 

 but also because he, too, noticed that the domatia of Coprosvia 

 were often tenanted by Acarids. He says : " In nearly all the 

 species except a few of the smaller-leaved ones, curious little pits 

 exist on the under surface of the leaves, in the axils formed by 

 the union of the primary veins with the midrib. They are never 

 more than ^ of an inch in length, and are usually much less. 

 Inside they are lined with numerous stiff white hairs, which on 

 being treated with caustic potash are seen to be composed of two 

 or three cells. So far as I have observed, the pits do not secrete 

 anything, and I am quite unable to guess at their function. They 

 are often inhabited by a minute yellow Acarid, which makes use 

 of them as a home. Sometimes two or three Acarids may be 

 found in the same pit, and they crawl freely about the young 

 leaves and branches." (Trans. N.Z. Inst. Vol. xix. p. 221.) 



