Keegan : The Haivfhorn. 



147 



infirmity whence springs the perhaps most remarkable feature 

 of the Hawthorn, viz., the extraordinary quantity of Hme which 

 it manages to absorb from the soil. It is never found growing- 

 naturally on a wet soil ; in fact, it flourishes most robustly on 

 a dry gravelly loam — a bottom where what may be called its 

 root-needs predominate and preside over as it were its very 

 existence. Gravelly clays and loams, although they may be 

 utterly free from carbonate of lime, are indispensable for the 

 pushing forth and proper functioning of certain roots and root- 

 lets. The remarkable feature is that, notwithstanding a 

 comparative poverty of the soil in lime, the Hawthorn never- 

 theless manages to absorb into its tissues an enormous quantity 

 of it. Thus, for instance, in October the buds are filled in 

 nearly all parts with oxalate of calcium which persists and 

 remains over the winter until the spring ; in the young leaves 

 numerous small druses of the same salt appear and grow in size 

 very rapidly, and are still present in the fallen leaves of autumn. 

 So likewise with the young shoot wherein druses first appear in 

 the pith, then in the primary cortex, and crystals in the bast, 

 which continuously increase in the course of summer, and in 

 winter reach nearly to the cambium. In general, the later 

 growth of the vascular bundles of branch and stem is accom- 

 panied by a separation of oxalate of calcium, and this has 

 a tendency to remain where it is originally formed and 

 deposited. Dead dried twigs and weather-beaten scales of 

 bark are found permeated with the same salt. In a section 

 of Hawthorn stem-wood in my possession several large octo- 

 hedral crystals of oxalate are seen scattered over the slide 

 occupying large thin-walled special sacs in the vicinity of the 

 vessels and medullary rays — a phenomenon quite unique in my 

 experience. The physiological function of oxalate of calcium 

 has been the bone of considerable contention. Some assume 

 that it is a fixed reserve-substance destined to be utilised b}^ the 

 plant later on, e.g., for the supply of cellulose-material for the 

 formation and thickening of the cell wall, etc. Others hold that 

 it is formed in those cells in which mucilaginous substances of 

 a chalky nature or pectin compounds are copiously accumulated, 

 it being developed entirely or mostly within the ambit, as it 

 were, of these bodies. Again, when the conditions of a very 

 active transpiration are especially favourable, then is the time 

 it has been asserted, that the oxalate depositing is most 

 pronounced ; but this view has been combated. Altogether, in 

 my opinion, the formation of the salt is due to an oxidation of 



1904 May I. - 



