Cockayne. — Ecological Studies in Evolution . 29 



juvenile stage of W. racemosa, or else that the former is the stem form and 

 W. racemosa a mutation or an epharmonic variant that has become fixed. 



Several instances of juvenile blossoming have already been given. The 

 following are additional examples : — Ranunculus Li/allii Hook. f. (the juve- 

 nile has a reniform leaf and the adult a peltate ; reversion leaves occur 

 as a result of bad nutrition ; there are intermediates between the two 

 types of leaves) : Pittosporum tenuifolium Banks & Sol. (the juvenile 

 seems to me identical with P. nigrescens Hort.,* the plant so much used in 

 certain parts of New Zealand for hedges ; as a hedge -plant the juvenile 

 form is alone to be seen, it being preserved by the constant cutting!) : 

 Clematis indivisa Willd. : Dracophyllum arboreum Cockayne : Agaihis aus- 

 tralis Salisb. : Nothopanax Edgerleyi Harms, (one semi-juvenile form blooms 

 and is the var. serratum T. Kirk) : and Anisotome filifolia Cockayne and 

 Laing. There are also a number of forest-trees which remain in the shrub 

 stage and flower (see Cockayne, 1908, p. 22). 



Each of the above cases would need deciding on its merits as to whether 

 the flowering juvenile might be the beginning of a new line of descent, or 

 was merely a reversion. I will only discuss the case of Anisotome filifolia 

 Cockayne and Laing. 



This is an herb with the leaves in an erect rosette and a long tap-root 

 which grows upon stony debris where there is a steppe climate in the moun- 

 tains of Nelson, Marlborough, and Canterbury. The leaves are grassy, 

 some 20 cm. long, ternately divided into segments which are filiform if 

 the plant grows in the open, but 3 mm. broad, or broader, when growing 

 in the shade. Both forms produce flowers. Seedlings raised from the fili- 

 form xerophytic form had broad segments (see fig. 38, pi. 12, in Cockayne, 

 1900, and also pp. 295 97). The broad leaves are certainly beneficial for 

 promoting rapid growth in a dry station, nor will the seedling be exposed 

 to as rigorous surroundings as the adult, protected as it will be by the 

 stones. Its form is therefore epharmonic. The broad-leaved adult of 

 the shade is then a flowering juvenile, which may or may not be " fixed," 

 but, if fixed, it would be an example of ontogenetic evolution, the arrival 

 of the new species dating from the first time the juvenile plant reproduced 

 its like from seed. 



Many of these heteroblastic species put forth when adult typical juvenile 

 or semi-juvenile shoots, as the case may be. Such may often be traced to 

 a special stimulus. Thus, stems of Phyllocladus alpinus Hook. f. when 

 prostrate on wet soil may bear abundance of true leaves, but those in a 

 drier position have phylloclades only ; Discaria toumatou Raoul cropped 

 by rabbits produces leafy shoots onlyj ; and Ranunculus Li/allii Hook. f. 

 grown in dry soil under unfavourable conditions may develop a certain 

 number of reniform seedling leaves. 



The position of the reversion shoots upon the plant differs in different 

 species. Very often they are confined to near the base, in which case they 

 may be merely developed resting buds. Pseudopanax crassifolium C. Koch 

 and Weinman-ma racemosa L. f. when cut to the ground regenerate from 

 the stump by means of juvenile shoots. Pittosporum tenuifolium Banks & 

 Sol., as a hedge-plant, remains permanently juvenile through frequent 



* H. M. Hall (1910) is of the same opinion. 



f Other species of Pittosporum also occur at times in these hedges through the 

 sowing of mixed seed, and so other forms of leaf may be occasionally present. 



% I noted one adult plant growing on a sand-dime that was almost, if not entirely, 

 without spines, the xerophytic station notwithstanding. 



