■;•] Kelly, 0]i the Function of Acacia Leaf Glands. 125 



only. We may also dismiss any suggestion as to these papillse 

 being embryonic cells. This may be disproved by unsuit- 

 ability of the tissue, and by the fact that, although acacias grow 

 on river-banks and the leaves fall in mud and other places 

 suitable for germination, no growth from them has ever been 

 recorded. With this my own experiments, conducted on the 

 assumption that everything is possible, have agreed. 



The three theories — symbiosis, fertilizing, and protective — 

 may be considered together, as either a fertilizing or protective 

 agency in this case would be intimately connected with insects, 

 and the symbiotic relation would be between the insects and 

 the plant. With a powerful lens no insect life can be observed 

 on the gland, nor in the cavity, even when opened by trans- 

 verse section. It might here be mentioned that the entrance 

 to the gland is very minute and (except in A. pyciiantha and 

 A. penninervis) protected by fine hairs, which, in addition to 

 other potentialities, prevent the access of water. The opening 

 in the pinnate species is generally roundish, but varies in different 

 species to diamond and triangular shapes. The inside of the 

 excrescence is hollowed out. In the large-leaved species, such 

 as Acacia pycnantha and Acacia pentiinervis, the cavity is 

 longitudinal, and almost closed up as if drawn lengthwise and 

 compressed in the process of rachis expansion. In A. pycnantha 

 the hollow of the gland is extended longitudinally in the edge 

 of the phyllode, and in it the crystals darken with age ; then 

 the glands turn brown. In these are no visible insects ; and 

 inside the hollow of A. penninervis the microscope discloses a 

 comparatively long green spike like a pistil with a knob on the 

 end. This spike projects from the side towards the centre of 

 the cavity, and extends nearly its whole diameter. Of many 

 species that I have examined, I have found insect life only in 

 two — Acacia Bailey ana and Acacia dealhata — and this only 

 by the aid of the microscope. They are extremely tiny 

 creatures, the identification of which rests with entomologists. 

 Most that I have observed are quite white and verv active ; 

 some are brown, and appear to colour with the discoloration 

 of their surroundings. I incline to the opinion that the 

 colouration of insects to suit their surroundings must be derived 

 from those surroundings, and that the colour of these insects 

 is derived from their food supply. They become darker as 

 their food does. They run in and about the crystals hke 

 people in streets. These insects are extremely difficult to 

 dislodge, and, being visible only under the microscope, it is a 

 work of art to get one for mounting. I have, so far, been 

 unable to trace their life-history, except that on the crystals 

 and the hairs outside I have found hanging their moulted skins. 

 I found the insects first in March of this year : in April they 



