78G DOMATiA IN CERTAIN AUSTRALIAN AND OTHER PLANTS, 



rate, it is certain that all the species having very perfect domatia 

 are so, and of these New Zealand, Lord Howe Island and Aus- 

 tralia supply a large i:)roportion. Out of 41 species named in my 

 original paper, 32 were from these localities. 



The most interesting question, however, is, What is the meaning 

 and purpose of these structures ? And it is a difficult one to 

 answer. The first possibility that occurred to me was that they 

 were pathological in their nature. But prolonged observation of 

 the plants and study of sections convinced me that they were not 

 so. I have seldom seen the slightest appearance of disturbance 

 of the tissues which form the walls and roof. In Packard's Forest 

 Insects (4) p. 554, there is a figure of a section of a Phjitoptus 

 gall from Fraxmus viridis which in outline resembles a domatium. 

 But it is only in general features that this resemblance holds — it 

 is quite different in details. Phijtoptus, too, spends its life in the 

 "all and can always be found there. But when a Phytoptus is 

 found in a domatium. Dr. Lundstrom observes and my own 

 experience coincides, that pathological changes are always present. 

 In Panax elegans and Moi'inda jasminoides I found domatia with 

 many Acarids — not Phytoptus — were diseased and altered, but it 

 was from the mites destroying the epidermis in the one case, and 

 in the other the appearance of the tissues was completely changed 

 from the normal state. At the same time I found leaves with 

 fully formed domatia, on the same twig and even at the same 

 node, opposite, which had no mites and were quite normal. 

 There was no doubt, therefore, that the diseased state was induced 

 in normal tissue by the insects. 



It next occurred to me that they might lie glands, and as many 

 of the plants bearing the highest type of domatia have extremely 

 glossy leaves {e.g., Coprosnia lucida), it seemed possible that they 

 might secrete resin or varnish. But an examination of all stages 

 of growth showed no secretion of any sort, nor did the structure 

 resemble that of any gland I know of, so that I abandoned this 

 line of inquiry. 



It was suggested to me that the domatia-bearing plants may at 

 one time have been like Banksia and Nerium, i.e., that their 



