I 



Cockayne. — Development of Seedlings. 357 



the seedling alone which so behaves ; but granted certain 

 conditions — notably such as produce rapid young growth — 

 and the mature plant will revert in part to the seedling form. 

 Some species are so unstable in form that both forms may be 

 found in a state of nature on the same plant at once — as, for 

 instance, when one portion is exposed to sun and wind, while 

 another portion is shaded. Thus at 1,500 m. on the Craigie- 

 burn Mountains I have found Veronica tetrasticha, Hook, f., 

 with both its scale-like''' and its true (seedling) leaves, the 

 latter occurring where a shoot was sheltered by a rock from 

 sun and wind. Many other examples could be adduced from 

 my own observations, but such will be reserved until dealing 

 with each particular species. 



Ku'k was the first to point out such dimorphism in the 

 whip-cord VeroJiicas (Trans. N.Z. Inst., vol. xi., p. 465), 

 statmg that " the dimorphism in the foliage of all the species 

 characterized by appressed leaves has not received the atten- 

 tion it merits. . . . There can be little doubt that the 

 free leaves are equally characteristic of the seedling state of 

 the plant, although I have been unable to find them in a wild 

 condition." That was published in 1878, but quite recently, 

 in the " Transactions of the New Zealand Institute " for 1895, 

 volume xxviii., page 515, Kirk again refers to the subject, 

 writing: "The species of the dimorphic — or, as it might with 

 equal propriety be called, the mimetic — section are invested 

 with special interest, the entire section, with the single ex- 

 ception of the Australian V. densifolia, being endemic in this 

 colony. At present, strangely enough, our knowledge of the 

 early leaves of these singular plants has been chiefly obtained 

 from old specimens, on which they are often produced by 

 reversion, especially under cultivation. The subject " [re- 

 ferring to the morphology of these species] " will not be satis- 

 factorily worked out until the seedlings, as well as the more 

 advanced stages, have been studied in a systematic manner." 

 Since such seedling leaves are usually developed on the 

 mature plant — as already pointed out — by conditions which 

 promote vigorous growth, can it be upheld, as a contrary 

 theory to such leaves being ancestral forms, that they are 

 merely special organs designed for the rapid growth of the 

 plant in its early and most insecure period of existence among 

 its often most inhospitable surroundings ? This might well 

 be a difficulty but for the fact that the early forms of a 

 seedling plant may be maintained even without specially 

 vigorous growth by giving the plant a certain environment 



* It was Mr. R. Brown (Brown ter.) who first demonstrated the true 

 character of the so-called leaves of that section of Veronica, ia a paper 

 read before the Horticultural Society of Christchurch, but not published 

 in any recognised scientific publication. 



