38 Transactions. 



present,* as in various instances of restricted distribution. Heat is a factor 

 of prime importance, and, so, many species have a definite southern or 

 altitudinal limit beyond which they do not extend {e.g., Agathis, Ipomaea. 

 Veronica elliptica, Knightia, Senecio rotundifolius, &c). This is not because 

 they cannot exist quite well farther to the south, or at a higher altitude, 

 but that on approaching their heat-minimum they cannot compete with 

 the other better epharmonically suited competitors. Further, changes of 

 land-surface have affected distribution in some cases, especially where they 

 have caused permanent or temporary barriers. 



The. annual number of rainy days is also a most important controlling 

 factor, and one whose effect is more plainly to be seen than that of heat. 

 The densely forested west of the South Island and the sparsely wooded 

 country beyond the average limit of the western rainfall to the east of the 

 main divide stand out in startling contrast. On the west the evergreen 

 canopy tree, and on the east the brown grass tussock, reflect in their respec- 

 tive dominance the prevailing ecological conditions. The slight differences,, 

 too, of the closely related Gaya Lyallii Hook. f. and G. ribifolia Cockayne 

 are excellent examples of quite small but distinctly epharmonicf distinc- 

 tions influencing distribution. 



Wind is another most powerful factor in New Zealand. According to 

 their relative wind-tolerating power do certain shrubs, &c, replace one 

 another on the shores of Paterson's Inlet, Stewart Island, so that the shore- 

 line has become in its vegetation an exact index of the frequency and velo- 

 city of the wind. The above steppe district in the centre and east of the 

 South Island is governed quite as much by the wind as by its moderate 

 rainfall. 



Quite common plants are extremely rare in certain localities. Cordy- 

 line australis Hook, f., a tree of physiognomic importance in many parts 

 of both the North and South Islands, occurs in only one locality in Stewart 

 Island. Leptospermum scoparium, usually so abundant, is represented by 

 but one or two individuals in the Chatham Islands, where there is the ideal 

 station for it to form a heath. J The tree-fern Hemitelia Smithii Hook., 

 so abundant in Stewart Island, is confined, so far as known, to one gully 

 in Auckland Island. Psychrophyton eximium Beauverd is abundant on low 

 alpine rocks on Mount Torlesse, Canterbury, but is wanting in similar 

 stations on the range on the opposite side of the valley. 



In some cases there is evidence that a plant has been much more 

 abundant, but has been replaced by another species. This is true " replace- 

 ment," and very different from the so-called replacement of indigenous 

 by introduced plants. Podocarpus spicatus R. Br. was an important 

 member of the Stewart Island forest, say, five hundred to a thousand years 

 ago. At the present time there remain only a few trees of that species, 

 but it is common to find old trunks of this taxad on which are growing 



* It is plain from the very nature of the case that perfect harmony can never be 

 established between the growth-forms and the habitat, since change, progressive or 

 retrogressive, is a feature of all formations, and growth-forms once epharmonic will 

 persist long after their epharmonic relation is weakened or destroyed. 



f G. Lyallii has larger, thinner, and much less hairy leaves than the eastern G. ribi- 

 folia. They have also drip-tips, which are frequently strongly developed. The juvenile 

 forms are somewhat similar in the two trees. 



\ This term " heath " I have used in my writings in default of a better, well knowing 

 the formation is not truly analogous, except after fire, with the heaths of Europe. By 

 the settlers, when full grown, it is known as " manuka " or " tea-tree scrub." At this 

 stage it is rather forest than heath. 



