Hollo WAT. — Six New Zealand Species of Lycopodium. 365 



nor is there any such correspondence to be traced in the strobiU. In the 

 large adventitious root., where the number of groups is from ten to fifteen, 

 the vascular arrangement is always radial. 



The development of stelar structure in L. densum was not traced in detail, 

 only one young plant being found. In this plant the stelar arrangement was 

 hexarch and radial, and there was no special rearrangement of stelar tissues 

 to be traced preparatory to branching. In the older stem of L. densum the 

 division of the stem stele preparatory to branching is always at right angles 

 to the plates of tissue. The aerial branches are often of strong growth, 

 and then the stele is stout ; in one case, in the oldest part of the branch, 

 the stele showed twenty-one protoxylem groups. In the oldest parts of 

 the branches the arrangement is generally " parallel," persisting from the 

 arrangement of the tissues at the branching of the main stem. Higher 

 up in the aerial branches the parallel gives place to a radial arrangement. 

 The many branchings of these aerial shoots are not restricted to one plane. 

 The arrangement of stelar tissues throughout the aerial branches is very 

 inconstant, and is in the older parts constantly passing backwards and 

 forwards from the parallel form to the radial. In the ultimate branchlets 

 there was no correspondence to be found between the number of ortho- 

 stichies of leaves and the arrangement of stelar tissues. 



The Mature Stele. 



Plates XXXIII and XXXIV are photomicrographs of the mature 

 steles of each of the six species considered in this present study. Of these 

 six species, the steles of all except L. Jaterale (Plate XXXIII, fig. 1) are 

 of exceptionally large size, and consequently most satisfactory to study as 

 types. Seeing that it is a characteristic feature of the genus Lycopodium 

 that there are to a greater or less extent continual changes going on in the 

 conformation of the stelar tissues, it will be seen that the larger the stele 

 the more satisfactory the example will it be of the particular type of arrange- 

 ment that it shows. L. cernuunt is well known as showing typically the 

 mixed arrangement (Plate XXXIII, fig. 2) ; L. Billardieri is a good example 

 of the radial type (Plate XXXIV, fig. 3), the mature stele showing from 

 nine to fourteen protoxylem groups ; L. volubile (Plate XXXIII, fig, 3), 

 L. scariosum (Plate XXXIV, fig. 1), and L. densum (Plate XXXIV, fig. 2) 

 rank as three of the largest of modern Lycopodiums, the number of proto- 

 xylem groups in the mature stele being — for L. volubile, 10-15 ; for 

 L. scariosum, 18-27 ; and for L. densum, 15-20. These three latter species 

 show typically the parallel type. 



Plate XXXII, figs. 1, 4, show clearly the difference between the mixed 

 and the parallel arrangements, both in the manner of disposition of the 

 protoxylem elements and also in the grouping and mutual coherency of the 

 "metaxylem elements. 



It is interesting to note that in the case of L. cernuum and L. laterale 

 the cortical tissues remain for the most part soft and parenchymatous 

 throughout the life of the plant. In L. Billardieri the outer region of the 

 cortex, and in L. volubile, L. scariosum, and L. densum from the very early 

 stage in the development of the plant, almost the whole of the cortical 

 tissue becomes sclerenchymatous. This enveloping zone of hard tissue 

 woidd no doubt tend to impart a certain degree of rigidity to the developing 

 stelar tissues, and may possibly bear some relation to the definite stelar 

 arrangement characteristic of these species. 



