274 DEFINITE ACTION OF THE Chap. XXIII. 



plants ; as a slight difference in the nature of the poison suffices 

 to produce widely different results ; and lastly, as we know 

 that the chemical compounds secreted by plants are eminently 

 liable to be modified by changed conditions of life, we may 

 believe it possible that various parts of a plant might be 

 modified through the agency of its own altered secretions. 

 Compare, for instance, the mossy and viscid calyx of a moss- 

 rose, which suddenly appears through bud-variation on a 

 Provence- rose, with the gall of red moss growing from the 

 inoculated leaf of a wild rose, with each filament symmetri- 

 cally branched like a microscopical spruce-fir, bearing a 

 glandular tip and secreting odoriferous gummy matter.^* Or 

 compare, on the one hand, the fruit of the peach, with its 

 hairy skin, fleshy covering, hard shell and kernel, and on the 

 other hand one of the more complex galls with its epidermic, 

 spongy, and woody layers, surrounding tissue loaded with 

 starch granules. These normal and abnormal structures 

 manifestly present a certain degree of resemblance. Or, 

 again, reflect on the cases above given of parrots which have 

 had their plumage brightly decorated through some change 

 in their blood, caused by having been fed on certain fishes, or 

 locally inoculated with the poison of a toad. I am far from 

 wishing to maintain that the moss-rose or the hard shell of 

 the peach-stone or the bright colours of birds are actually due 

 to any chemical change in the sap or blood ; but these cases of 

 galls and of parrots are excellently adapted to show us how 

 powerfully and singularlj^ external agencies may affect struc- 

 ture. With such facts before us, we need feel no surprise 

 at the appearance of any modification in any organic being. 



I may, also, here allude to the remarkal^le effects which parasitic 

 fungi sometimes produce on plants. Eeissek^^ has described a 

 Thesium, affected by an CEcidium, which was greatly modified, and 

 assumed some of the characteristic features of certain allied species, 

 or even genera. Suppose, says Eeissek, " the condition originally 

 " caused by the fungus to become constant in the course of time, 

 " the plant would, if found growing wild, be considered as a distinct 

 " species or even as belonging to a new genus." I quote this 



^* Lacaze-Duthiers, ibid., pp. 325, by Dr. M. T. Masters, Royal Institu* 

 328. tion, March IGth, 18()0. 



" 'Linnsea,' vol. xvii., 1843 ; quoted 



