Hollo WAT. — Six Xeiv Zealand Species of Lycopodium. 369 



as showing radial symmetry, and notes that L. Dalhousieanum, L. phleg- 

 maria, and L. nummular i folium also conform to this type. L. Billardien, 

 the epiphytic species studied here, also shows typically the radial arrange- 

 ment. 



The following points call for consideration as suggesting that the parallel 

 type is but a specialisation from the radial type consequent on the restric- 

 tion of stem-branching to one plane : (1.) The distinction between the two 

 types of arrangement is not very great, as was seen from the ease with which 

 one can pass into the other in L. volubile, L. densum, and L. scariosum. 

 (2.) In L. volubile and L. scariosum the parallel arrangement makes its first 

 permanent appearance in connection with the forking of the stele, it being 

 an invariable rule that the disposition of the plates of tissue is always at 

 right angles to the plane of stelar forking. (3.) In those parts of L. volubile 

 and L. scariosutn and L. densum where branching takes place in any plane — 

 namely, large adventitious roots of all three species, and aerial branches 

 especially of L. densum — parallel arrangement is either wholly absent (as 

 in the former) or may be seen in the act of passing back into the radial (as 

 in the latter). 



III. The Difference between " Mixed " and " Banded " Types. 



The view is here taken that whereas the parallel banded may be regarded 

 as but a specialised form from the radial banded, the difference between 

 the " mixed " and the " banded " types is far more deeply seated. The 

 study of the early stages of L. cermium and L. laterale on the one hand, and 

 of L. volubile and L. scariosum and L. Billardieri on the other, reveals the 

 fact that from the very first the stele of the two former shows the " mixed " 

 arrangement of its tissues, whilst the stele of the three latter shows 

 a very definite " banded " arrangement. The particular arrangement, 

 then, that each shows may be regarded as belonging to its inherited con- 

 stitution. 



The question arises, l ""s the nature of the dependence of the young plant 

 upon its prothallus any significance in this connection ? In the case of L. 

 cernuicm and L. laterale the prothallus is very short-lived and small, and 

 the young plant is called upon to begin its work of assimilation at once ; 

 hence the first-formed vascular tissues in the plant is the leaf-trace system, 

 and for a considerable time in the development of the plant the indiscri- 

 minate arrangement of the leaf-traces in the stem determines the natvire 

 of the stelar arrangement. In the case of L. volubile and L. scariosum 

 and L. Billardieri the prothallus is long-lived, and the young plant feeds 

 upon it for a long time ; hence the plerome cyhnder becomes strongly 

 developed, and the leaf-traces, when they appear, affix themselves definitely 

 to the compact protoxylem groups. This is probably the case also in 

 L. densum. 



Another point worthy of attention is with regard to the effect upon the 

 developing stelar tissues that a zone of cortical sclerenchyma may have. 

 In L. volubile, L. scariosum, and L. densum there is a well-developed sclerotic 

 region in the cortex in the young plant, and this soon comes to embrace 

 the whole of the cortex. In L. cernuum there is no such region, and but a 

 feebly developed one in L. laterale. Possibly the presence of such a region 

 enveloping the developing stelar tissues may serve, by imparting rigidity 

 and lateral pressure to the tissues, to insure the greater coherency of the 

 xylem elements into groups and bands. 



