124 Kelly, On the Function of Acacia Leaf Glands. [v^J|^''\>^x 



missed, in view of the fact that nature would scarcely duplicate 

 structures for the one office, and of the further fact that glands 

 in pinnate leaves would be limited to the control of the pinnae 

 between which they are situate, and that in many species and 

 individuals there are pinnae with no glands to control them, 

 and that in phyllodes this use would be vacated. 



The further theories which required consideration were :— 

 Are these structures — {a) stomatoid growths, (6) assimilative 

 organs, (c) stipular growths, {ci) symbiotic organs, {e) fertilizing 

 aids, (f) protective aids ? That these may, in the main, be 

 considered together, I will quote the only passage that I have 

 been able to discover in any authority directly bearing on the 

 subject — viz., Solereder (Solereder, " Systematic Anatomy of 

 Dicots.," Boodle and Fritsch, vol. i., page 296, 1908) : — 

 " Rather large peltate or wart-hke masses of tissue occur on 

 the petiole of most Mimoseae. These are visible even with the 

 naked eye, have secretory functions, and, as they are easily 

 observed, have already been described by systematists (see 

 Delpino). Without deahng more fully with the diverse 

 structural features of these petiolar glands, it need only be 

 stated here that they consist of a parenchymatous group of 

 cells below which bundle-terminations, with abundant deposi- 

 tion of crystals in the surrounding tissue, usually occur. They 

 are occasionally (in the acacias possessing phyllodes) reduced 

 to glandular spots, and sometimes excrete a sap containing 

 sugar." I have not had the advantage of seeing Delpino's 

 work, nor any further comments thereon nor extracts there- 

 from. 



Regarding the stomatoid growths, the only relation that can 

 be suggested is that, as acacias have practised economy of 

 transpiration and the retention of moisture over long periods, 

 the restriction of evaporation has caused an accumulation of 

 deposit in the form of sugar or other crystals. This, in the 

 coarser portion of the plant, is exuded as gum, and in the leaves 

 through these glands, and by pores on the leaves for cleaning 

 the finer cuticle. This residuum is found in the crystals of 

 the glands and the waxy deposit on the leaves ; in the last 

 case, at least, being put to an economical protective use, making 

 cause and effect serve the same or aid the one purpose. This 

 would point to the so-called glands being excretory organs. 

 In this capacity they would also have in one sense assimilative 

 functions, in being clearing-houses of excess substances. The 

 last two stages of this form of excretion of residuum does not 

 take place, and is unnecessary, in gum-yielding, deciduous trees, 

 such as the common cherry. These growths are only analogic- 

 ally stipular, and are rudimentary relics. This theory in no 

 way, however, affects their present function, but is historical 



