

284 



DEFINITE ACTION OF THE 



Chap. XXIII. 



agent 



in 



dete 



the for 



As 



of the tree which is acted 

 poisonous secretion of insects bel 



of the gall than the specific 



orders has the special power of affecting the growth of 



plants 



slight difference in the nature of the poison suffi 



produce widely different results ; — and lastly, as we know that 



3 chemical compounds secreted by plants are eminently liable 



be modified by changed conditions of life, we may believe 



possible 



parts of 



a 



plant 



might 



through the agency of its own altered 



be modified 

 Compare, for 



instance, the mossy and viscid calyx of a moss-rose, which sud- 

 denly 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 symmetrically branched like a inicro- 



•pical spruce-fir, bearing a g 



landular tip and 



ifer 



fr 



ummy matter. 53 Or compare 

 of the peach, with its hairy skin 



on the 

 fleshy 



h ard 



shell and kernel, and on the other hand one of the more 



compl 



g 



with 



pidermic 



y, and woody lay 



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 



fishes 



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 



tually due to any chemical chan 



the sap or blood 



but these cases of galls and of parrots are excellently adapted 



t 



how powerfully and 



may affect structure. W 



■ly external agencies 



such facts befor 



feel 



us, we n 



eed 



no 



pr 



o 



se at the appearance of any modification in any 

 organic bein 



I may, also, here allude to the remarkable effects which parasitic fungi 

 sometimes produce on plants. Eeissek M lias described a Thcsium, affected 

 by an (Ecidium, which was greatly modified, and assumed some of the 



53 Lucaze-Duthiers, idem, pp. 325, 328. 



64 'Linnsea,' vol. xvii., 1843; quoted by Dr. M. T. Masters, Royal Institution 

 March 16th, 1860. 



? 



