82 Transactions. 



II. The Isolation of Portions of Lateral Branches or of the Main 

 Axes of the Plagiotropic Species. 



This method of spreading is commonly found in all the plagiotropic 

 species of the genus. The young prothallial plants are orthotropic in the 

 case of all the New Zealand species whose adult plants have this plagio- 

 tropic habit of growth, but sooner or later they adopt the latter habit. The 

 main axis, which in some species is subterranean and in others above ground, 

 is generally speaking of unlimited growth, as are also certain of the lateral 

 branches. Adventitious roots arise at intervals from the dorsal surface 

 along both the main axis and the lateral branches. The vegetative spread 

 of such a species takes place by the dying-away of the older parts of the 

 main stem or by the isolation of the lateral branches. It is obvious that 

 the form and habit of the plagiotropic species are adapted to this method 

 of propagation. 



The plagiotropic species of Lycopodium are thus most fitted for rapid 

 extension over new areas. These are the species found in large spreads 

 over recently disturbed areas, such as forest clearings, roadside cuttings, 

 sluiced goldfields, &c. This method of propagation is in all probability 

 the main one in these species, except perhaps in the initial establishment 

 of the species in the new area. Germination of the spores of these species 

 does readily take place where the right conditions are present, but the 

 delicate nature of the prothallus of some of them {e.g., L. cemuum, L. laterale, 

 and L. ramulosum), and the unusual length of time required for the full 

 development of the prothallus of others (e.g., L. fastigiatum, and also L. 

 volubile, L. scariosum, and L. densum), are the reasons why only in exceptional 

 localities, or during an exceptional series of seasons, are sexually produced 

 plants firmly established. In Westland, where the rainfall is extremely 

 high, I have frequently found in many localities colonies of young plants 

 of the species L. fastigiatum, L. volubile, L. scariosum, and L. ramulosum 

 which had been sexually produced, and of which a considerable proportion 

 had come to maturity. In those parts of Canterbury and Nelson, howver, 

 where dry seasons are common I have on several occasions come across 

 colonies of the young plants of L. fastigiatum, L. volubile, and L. scariosum 

 which had become dried up. And on the clay gum -lands of Auckland, 

 which are generally subject to being dried up in the summer, and where 

 the two species L. cemuum and L. laterale commonly occur, it is probable 

 that the young plants, which I have frequently found together with the 

 prothalli, rarely come to maturity. 



The form and habit of the plagiotropic species are probably to be 

 regarded as a direct adaptation to the environment. The anatomical struc- 

 ture of the stem will also be modified in accordance with this. I have 

 shown (1910, pp. 362-64) that the development of the parallel structure in 

 the vascular cylinder of the developing stem of L. volubile, L. fastigiatum, and 

 L. scariosum is the direct result of the restriction of branching to one plane. 

 We may, of course, expect to find that the plagiotropic habit of growth 

 has been evolved in species which belong to different natural sections of 

 the genus. The fact that in the plagiotropic species there are at least two 

 main types of stem vascular anatomy- — viz., the " mixed " type of L. cemuum, 

 (and also L. laterale, L. ramulosum, and L. Drummondii), in which the xylem 

 and phloem elements are intermingled and present no definite structure, and 

 the " parallel " type of L. volubile (and also L. scariosum, L. fastigiatum. 

 and L. densum), in which the vascular elements are disposed in parallel 

 plates — is an indication that the species which conform to one type are to 



