1890.] Mr Gardiner, On Acacia sphaerocephala. 65 



March 10, 1890. 

 Mr J. W. Clark, President, in the Chair. 



The following Communications were made to the Society : 



(1) On the germination of Acacia sphaerocephala. By 

 W. Gardiner, M.A., Clare College. 



[Reprinted from the Cambridge University Reporter, March 18, 1890.] 



Seeds of this well-known myrmecophilous plant have been 

 lately germinated, both at Kew and Cambridge, affording oppor- 

 tunity of observing seedlings in all stages of growth. The striking 

 manner in which this plant exhibits definite structural adaptations 

 for the benefit of the ant colonies, which so efficiently garrison it, 

 has suggested that the structures in question possibly owe their 

 formation to the action of the ants themselves, and arise in con- 

 sequence of local stimulation produced by biting (when in search 

 of sweet sap) or even by stinging. Actual observation shows that 

 as the seedlings assume the adult foliage, the stipular thorns, the 

 petiolar glands, and the "food bodies" all develoj>e quite normally, 

 and in spite of the ants being absent. It is clear therefore that 

 in plants which exist at the present time the structures appear 

 without the intervention of ants. It may, however, be urged that 

 they were in the first instance brought into existence by ants, 

 through the stimulation of ancestral forms, such stimulation 

 having been persistent and extending over many generations. 

 A study of germinating seedlings does not appear to support this 

 view. The development of the several structures can be traced 

 so gradually and through so many transition forms that there 

 appear to be strong grounds for believing that the whole of the 

 complicated arrangements and of the several organs concerned 

 are the outcome of variation, and that the ants have done little 

 more than take advantage of the results of such variation. More- 

 over no absolutely new organs are present, the thorns being as 

 well, or even better, developed in other species of Acacia; e.g. 

 Acacia latronum: the petiolar nectaries being well known and 

 common structures : and the food bodies (as their development 

 shows) being hypertrophied " Reinke's glands." 



(2) Additional note on the thickening of the stem in the 

 Cucurbitacege. By M. C. Potter, M.A., St Peter's College. 



Hitherto very few Dicotyledons have been described which 



possess a ring of normal collateral bundles and whose stem at 



the same time does not increase in thickness by means of a 



cambial ring. De Bary 1 mentions under this category the Saururew 



1 Comp. Anat. Eng. Ed. p. 454. 



