Cockayne. — Ecological Studies in Evolution. 23 



of plants of this class may grow side by side belonging to the genera Dacry- 

 dium, Podocarpus (Taxac), Leptospermum (Myrtac), Styphelia (Epacrid.), 

 Coprosma (Rubiac), Veronica (Scrophular.), and Celmisia (Compos.). In 

 some cases the prostrate form is here hereditary, while in others it is unfixed 

 and depends merely upon the station. 



The combination of species forming the shrub steppe on the subalpine 

 volcanic plateau, North Island, contains a considerable percentage of 

 prostrate shrubs, some of which are more or less erect under less xero- 

 phytic conditions. 



Coastal rocks favour the prostrate form. Thus in such a situation 

 near Island Bay, Wellington, there are Hymenanthera crassifolia Hook. f. 

 (more or less hereditary), Coprosma Baueri Endl. (hereditary when juvenile), 

 Veronica macroura Hook. f. var.* (perhaps hereditary when juvenile but 

 erect when adult). 



Other veronicas of coastal rocks are more or less prostrate, and this 

 is strongly hereditary in V. chaihamica Buchanan — so much so that a shoot 

 grown verticallv in a pot quickly assumed the horizontal direction (see 

 Plate V, fig. 1). 



An interesting instance of non-hereditary convergent epharmony of 

 this growth-form is the wiry undergrowth of three species of Coprosma 

 beneath the tussocks of Danthonia antarctica Hook. f. at some 250 m. 

 altitude in Auckland Island. One of the species, C. foetidissima, is 

 " normally " a tall twiggy shrub, and the other two are medium-sized 

 divaricating shrubs. 



6. Persistent Juvenile Forms. "f 



About two hundred species of New Zealand vascular plants, belonging 

 to thirty-seven families, show a more or less well-marked distinction 

 between the juvenile and adult stages of development, while in perhaps 

 one hundred species the differences are very great indeed. The most 

 interesting cases are those in which a juvenile form remains permanent 

 for a number of years, so that in its ontogeny the individual passes through 

 two, or even more, distinct stages, and not infrequently through two 



* I am inclined to think it would be better to consider' this a species. It differs 

 considerably from the typical form, which grows in the East Cape district. 



f Heteroblastic development is a world-wide phenomenon which has not received 

 nearly the attention it deserves from writers on evolution. It is its occurrence in so 

 many endemic species in New Zealand that makes data from this region of special interest. 

 In 1879 I. Bayley Balfour recorded a number of striking examples from the Island of 

 Rodriquez — e.g., Clerodendron laciniatum Balf. f., reminding one of the New Zealand 

 Nothopanax simplex Seem. ; Pyrostria trilocidaris Balf. f. ; Fernelia buxi folia Lam., a 

 rubiaeeous plant, evidently when juvenile somewhat of the divaricating shrub form : 

 and Mathurina pendidiflora Balf. f. (Turnerac), which has long narrow juvenile and 

 broad adult leaves, as in Parsonsia heterophylla A. Cunn. and other New Zealand plants. 

 Altogether seventeen species of trees and shrubs and one herb out of 175 species of 

 spermophytes show marked dimorphism. Goebel (1889-93) gives a number of examples 

 of heterophylly, &c, referring the phenomena in some instances to direct outer stimuli, 

 and he deals further with the matter in his " Organography of Plants " (19CC-5) and 

 his " Experimen telle Morphologie " (1908). Diels (190G) goes into the matter at con- 

 siderable length, using many important illustrations from his observations in Western 

 Australia. As for the phenomenon in New Zealand, Hooker was the first to refer to it, 

 in his splendid " Introductory Essay to the New Zealand Flora " (1853, p. 1). Kirk gives 

 many details in his " Forest Flora " (1889), and these are supplemented by Cheeseman 

 in his Manual. Finally, my own writings since 1899 contain a good deal of scattered 

 information not previously published. 



