272 Transactions. — Botany. 



ribifolia — I append only the varietal name, partly for sake 

 of brevity and partly because it seems to me a perfectly dis- 

 tinct species, as Mr. D. Petrie suggested to me so long ago^ 

 as January, 1893 — vary considerably and are of two types : 

 First, those which come close to the seedling leaves and are 

 deeply lobed, sometimes of greater breadth than length and 

 with the apex rounded and little drawn out ; second, those of 

 an ovate outline, with an apex much more acuminate, and 

 with the lobes less deeply cut into the leaf than in the 

 seedling forms, a leaf much resembling that of Gaya lyallii. 

 In specimens from the Kaikoura Mountains the leaves are 

 lobed much less than in my Canterbury specimens, and their 

 apices are still more acuminate. All the adult leaves of Gaya 

 ribifolia are covered on the under-surface with a mat of stellate 

 hairs (Plate XII., fig. 46), which gives a whitish colour to that 

 surface of the leaf, and almost hides the reticulating veins. 

 The western plant, on the contrary, is bright apple-green on 

 both surfaces, the stellate hairs being confined mainly to the 

 principal veins. The individual hairs, moreover, are usually 

 about half the length of those on the eastern plant. This 

 difference in colour enables a thicket of either form of plant 

 to be identified at a glance, even when the observer is quite a 

 distance away. The western plant has its adult leaves not 

 lobed, but only irregularly toothed, and the apex is always 

 much drawn out. 



I have not up to the present critically studied Gaya 

 lyallii in the seedling form, but reversion leaves of that 

 species are almost identical with some of the seedling leaves 

 of G. ribifolia above described, and this shows that the two 

 forms are very closely related ; while possibly the more 

 glabrous western form may be the ancestor of the tomentose 

 eastern form, whose tomentum is clearly an adaptation to the 

 drier character of its station. It is cecologically of extreme 

 interest that a character seemingly so trivial as a slight varia- 

 tion in hairiness of leaf has led to these two species not 

 having intermingled, although they approach in places to 

 within only three or four miles from one another at most ; 

 and it shows, moreover, how an apparently unimportant 

 character may govern the climatic distribution of a plant.* 

 It may also be pointed out that both forms thrive equally 

 well side by side in lowland gardens where the rainfall is 

 slight, and that the characters of each, so far as I have been 

 able to ascertain, remain unchanged. 



* In a struggle for existence between these two plants it seems prob- 

 able that each in its own domain would wipe out the other, unless the 

 invader possessed a special power of rapid adaptation to the new con- 

 ditions. 



