E. R. Saunders 173 



Massart considers that in these circumstances it is difficult to hold that 

 this character is inherited at all, and sums up the position with the 

 statement that the more free a species is from the shackles of heredity 

 the greater is its faculty for accommodating itself to the environment. 

 In the light however of what we know from genetic analysis in other 

 cases we may view the above facts from a somewhat different standpoint. 

 We may presume that in Polygonum when submerged, and in Ranun- 

 culus when growing out of water, the hereditary mechanism is unable to 

 bring about the physiological conditions necessary for the development 

 of the hairs in question. The portion of the mechanism immediately 

 concerned in the formation of scutiform hairs in Polygonum may be 

 looked upon as in a state of such stable adjustment that its working is un- 

 affected by changes in the external medium ; it is always effective. But 

 another piece of the mechanism involved in setiform hair production may 

 be imagined to be so delicately balanced that a change of environment 

 causes a readjustment from a hair-producing to a non-hair-producing 

 state of equilibrium, or vice versa. To this extent we may agree that 

 inheritance is not shown. But if the requisite physiological condition 

 for hair development is set up by suitable environmental conditions the 

 hereditary mechanism comes into play, determining the form (and in 

 Ranunculus the position also) of the hairs. In the same way we may 

 explain the effects which result in certain plants from injury. Injury 

 in the case of a hairless form may result in the setting up of an altered 

 condition of physiological equilibrium which permits of hair formation, 

 the character of the hairs which result, however, being clearly determined 

 by some hereditary process. It is stated, for example, that galls formed 

 on the glabrous species Vitis vulpina and V. cordifolia show hairs 

 resembling those forming the tawny tomentum of V. aestivalis and 

 V. Labrusca ; and that hairs produced through insect activity on smooth- 

 leaved Oaks are of the stellate type ordinarily found in hairy-leaved Oaks^ 

 and other instances could be given. In this connection may also be 

 mentioned the interesting results obtained by A. W. HilP with Tro- 

 paeolum peregrinum L. (Canary-creeper). Hill found that it was possible 

 to induce this glabrous species to develop hairs by removing the lamina 

 of the leaves, leaving only the mid-rib. In none of these cases, however, 

 do we yet know the exact nature of the change which is induced. 



The expenses incurred in connection with this work have been 

 defrayed in part by grants from the Royal Society and from the British 

 Association for the Advancement of Science. 



1 See Coulter, Barnes, and Cowles, Textbook of Botany, Vol. ii, p. 575, 1910-11. 



» Annals of Botany, Vol. xxvi. 1, p. 589, 1912. 



Joom. of Cren. x 12 



