788 DOMATIA IN CERTAIN AUSTRALIAN AND OTHER PLANTS, 



experiments by waxing cut petioles, letting the leaf wilt and then 

 weighing and immersing in water, at the same time treating 

 leaves of the same area, weight and consistence in a similar way. 

 I found that both kinds of leaves gained in the same ratio, from 

 5 to 20 per cent., so that the domatia-bearing leaves had no 

 advantage. I tested them in the same w^ay for the absorption of 

 vapour in closed moist chambers, in sunlight, diffused light, and 

 darkness. The results were contradictory in both kinds of leaves. 

 Some gained 1 per cent., and others lost as much or more. At 

 that time I was under the impression that stomata did not occur 

 in the pits, but as has been shown, this was a mistaken view. 

 For want of a quantity of material I did not experiment on these 

 plants. But it must be remembered in this connection that the 

 stomata are in no way different nor more abundant relatively in 

 the pits, and as there are thousands on the free surface of the leaf, 

 no great advantage could accrue from the pi^esence of a few in 

 sheltered pits. 



Dr. Lundstrom in considering their use took up the possibility 

 of their being connected with motile phenomena, but found that 

 untenable. He also considered them as being perhaps insect 

 traps, but was compelled to abandon that view also, as the mites 

 go in and out freely. In this my experience coincides with his. 



The final conclusion he came to w^as that we have here an 

 instance of symbiosis between the plants and the mites, and he 

 thinks that the production of incomplete domatia has become 

 hereditary in these plants, the stimulus given by the arrival and 

 presence of the mites causing the final development of the 

 domatia. He was led to this from observing the almost universal 

 presence of mites in the cavities — in which I cannot say that my 

 experience coincides. I find mites sometimes, but just as often 

 not, and in the two instances in which I found large numbers 

 (before referred to) I found the domatia damaged by them. He 

 claims that mites of the type figured by him do not damage the 

 cavities, but that Phytoptus mites do. But in both the instances I 

 speak of the mites were remarkably like those figured, and most 

 certainly were not Phytoiytii^s. In answer to the question of what 



