HoLLOWAY. — Six New Zealand Species of Lycopodium. 361 



L. volubilf, L. scariosiDn, and probably, too, L. densuni, may be taken as 

 corresponding to the type of L. clavatum in the mode of dependence of the 

 young plant upon its prothallus. 



Early Stages in Development of Vascular System. 



The earliest stages were traced in the case of L. cernuum and L. laterale. 

 A few spiral tracheids and phloem elements become differentiated at the 

 base of each protophyll. These elements extend downwards into the region 

 of the protocorm. where they end blindly. 



The vascular system of the stem axis originates from the leaf-traces, 

 which aggregate loosely and indefinitely at the centre of the stem. Later, 

 when a plerome cylinder develops, the leaf-traces affix themselves to its 

 periphery. Transverse sections of stems of young plants of these species 

 at this stage show that there is no definite arrangement of the vascular 

 tissues, the different xylem and phloem elements preserving no constant 

 relative positions. The vascular tissues of the stem lead down bodily into 

 the upper region of the protocorm, and, surrounded by a slight zone of 

 sclerenchyma, enter the root-like protuberance, in the case of L. laterale 

 passing along the dorsal surface of the protocorm immediately beneath the 

 epidermis. In the young plant of both these species the leaves are very 

 numerous and irregularly arranged. The leaf - traces attach themselves 

 indiscriminately to the periphery of the plerome cylinder, forming later an 

 almost continuous ring around the central vascular tissues. 



In the three species L. BiUardieri, L. volubile, and L. scariosum the 

 .stems of the youngest prothallial plants sectioned were from |-1 cm. in height, 

 being simple, erect, cylindrical, and apparently destitute even of scale 

 leaves. In these species vascular tissues are developed as a plerome cylinder 

 in the stem of the young plant before either leaves or first root appear, and 

 function probably in transferring food material from the prothallus to the 

 growing regions of the stem. In the young stem of L. BiUardieri the first 

 stage in the development of the stele shows a single compact somewhat 

 crescentic-shaped group of protoxylem enclosing a single group of proto- 

 phloem. In both L. volubile and L. scariosum the stem stele from the very 

 first is compact, and the arrangement of its tissues definite ; in L. volubile 

 it at first shows two protoxylem groups, between which is a single group of 

 jDrotophloem. Plate XXXIf, fig. 2, is a drawing of the stele of a young plant 

 1 cm. high and destitute of leaves. In L. scariosum from the first the stele 

 is of larger size, and the protoxylem and protophloem more strongly de- 

 veloped than in the young plant of L. volubile. The first stages show from 

 3-5 protoxylem groups. Plate XXXII, fig. 3, shows the stele of a young plant 

 1^ cm. high, and destitute of leaves. The very early stages in the develop- 

 ment of the stem stele of L. densum were not observed, but they will pro- 

 bably be found to correspond closely to those of the two last named species, 

 since in other ways the young plant of L. densum corresponds closely to the 

 type of L. volubile and L. scariosum. 



It will thus be seen that two distinct types of arrangement of the vas- 

 cular tissues in the very young stem are shown by the study of the above 

 six species — namely, the loose indefinite type of L. cernuum and L. laterals 

 and the more compact definite type of L. BiUardieri, L. volubile, and L. 

 scariosum. These two types of stelar arrangement would seem to be, to 

 some extent at least, correlated with the two types of leaf-trace system 

 shown in the young plants of these species. In L. cernuum and L. laterale 



