206 Transactions. 



In the Selago and Phlegmaria sections, owing to the fact that the primitive 

 dichotomous nature of branching is the characteristic one, the plant is strictly 

 limited in size. In the Inundata and Cernua sections both dichotomous 

 and monopodia] branching is to be found. The branching of the young 

 plant of L. cernuum., L. latemle, and L. ramulosmn is always at first 

 dichotomous. In L. ramulosum this is more or less maintained throughout 

 the life-history, the rosette form which arises as the result of the repeated 

 dichotomies being very characteristic. This species shows an interesting 

 transition from the subaerial to the subterranean habit of growth, the 

 branches in some localities growing down into the soil and functioning as 

 rhizomes. In L. laterale this has taken place to a greater extent, so that 

 there the branches of the plant have become permanently subterranean. 

 However, in this species also the growth of the plant is limited, for sooner 

 or later these rhizomes emerge from the ground as the aerial shoots. The 

 branching of the mature plant of L. Drummonclii, however, is monopodia!, 

 and the plant itself is wholly above-ground, so that the way is open for 

 it to spread extensively ; but it never attains a greater length than 6 in. 

 to 8 in. All the members of the Inundata and Cernua sections are very 

 limited in their extent of growth, except L. cernuum, the replacing in them 

 of the dichotomous by the monopodial habit of growth resulting in very 

 little increase in the size. In L. cernuum, however, the case is different. 

 Here too the branching is dichotomous in the young plant, but the adoption 

 of the monopodial habit leads to the unlimited growth both of the main 

 stem and of some of its lateral branches. This species alone of those which 

 belong to these two sections spreads itself over dry localities, the others 

 being all confined to a marshy habitat. It would seem best, then, to regard 

 this character in L. cernuum as quite a recent adaptation, this species, at 

 any rate with respect to its habit and external form, being by no means 

 typical for the two sections. The trailing habit of L. cernuum is not so 

 characteristically plagiotropic as is that of the species comprising the 

 Clavata section. It provides in this respect a transition, for its main stem 

 is more ascending than creeping. The apex is continually striving to ascend, 

 and it is only through being weighed down to the ground through its own 

 increase in length that the stem then puts forth a bunch of adventitious 

 roots, the series of such loops in which the plant grows showing that it 

 consistently maintains the ascending habit. Amongst the Leptospermum 

 scrub in the gum lands of North Auckland, where this species grows most 

 luxuriantly I have sometimes seen the stems scrambling over the vegeta- 

 tion. However, this is by no means so marked a habit as in L. volubile, in 

 which latter species striking modifications have taken place as a result of 

 this habit. 



In the young plants of the species which comprise the Clavata section 

 the monopodia! habit of branching is present before ever the young plant 

 becomes plagiotropic ; in fact, in most cases there is no dichotomous 

 branching at all (16, figs. 97-101). The terminal region of the main stem 

 suddenly assumes a stouter form and puts forth an adventitious root. 

 This most often takes place after the plant has begun to bend over. If 

 we are to argue from the facts of the ontogeny we must certainly con- 

 clude that the plagiotropic habit of growth is a recent adaptation, and 

 that the power of unlimited growth is the most recent feature of this 

 habit. This is the conclusion also to which the facts relating to the 

 Inundata and Cernua sections seem to lead us. There is one feature 

 which probably is a still further adaptation, and that is the subterranean 



