Nov 



J°j^'^'] 'K'ELi.Y, On the Function of Acacia Leaf Glands. 123 



lie along the midrib immediately below the flowering spike or 

 raceme, and in phyllodes on the edge in a corresponding position 

 — e.g.. Acacia melanoxylon. Acacia pycnantha, Acacia pennineyvis, 

 Acacia cultriformis — and at any rate in those with only one 

 head on a peduncle the flower-head deflects laterally from this 

 position in fertihzation. Is this position merely an insignificant 

 coincidence ? 



The flowers of Acacia dealhata ?ind. Acacia Nataliiia lie more 

 obhquely above the leaf. A few glands were lined with a fine 

 cobwebby substance, such as forms the cocoon of some insects. 

 Many of the tender ones appeared to be bitten by an insect, 

 but so also did the pulvinus and the pinnae ; but I could find 

 no cases of this biting in any glands on the leaves below a 

 flower-head of Acacia Nataliiia, whether deflected or not, yet 

 these were apparently more tender and edible. T may here 

 note that in Acacia melanoxylov, bearing both phyllodes and 

 pinnate leaves, and also the leaf combining both phyllodes and 

 pinnae, the gland was situated always on the phyllode and never 

 on the rachis of the leaf, unless that rachis were well extended 

 laterally, and then only on the outer edge. No physical inter- 

 ference with the leaves, glands, or pulvinus was productive of 

 leaf-sleep in Australian species, but severance of the leaf, and 

 even touch, caused the pinnae of several African species to 

 close almost immediately, yet nothing indicated definitely that 

 the gland had any part in this. 



There were in my mind during the pursuit of these inquiries 

 several theories as to function. The first, that they may be 

 gangha, has been practically disposed of ; suffice it further to 

 say that the pulvinus or thickening at the base of the petiole, 

 so general in leguminous plants, has some of the characteristics 

 of nerve-controlled tissue, and its function is generally supposed 

 to be the control of leaf-sleep. If this function is exercised by 

 the pulvinus, why not by the glands ? This proposition is 

 partly answered by the fact that other plants, such as Robinia, 

 have no glands, and are controlled sufficiently by the pulvinus. 

 We have, as far as I have been able to discover, no adequate 

 explanation of the action of the pulvinus — how it acts, nor 

 what conveys to the contractile tissue the stimulus of light, 

 heat, cold, or other shock. That there are sensitive plants, 

 such as Mimosa pudica and the Styhdeae (trigger-plants), is 

 certain ; but, as to their nervous character, the knowledge seems 

 to be quite empirical. There is no certainty that sensitiveness 

 of plants is of a nervous nature, nor, if so, where nervelessness 

 in plants merges into nervousness, nor whether this latter 

 character in any way approximates to the elemental nerve 

 system in animals. Under these circumstances, it is diflicult to 

 pursue that theory further, but the probability may be dis- 



