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there being an inner slightly sclerenchymatous zone, which is more strongly 

 developed in the aerial branches, merging outwards into a thin-walled 

 spongy tissue which is continued right up to the epidermis. In dissecting 

 out the rhizomes of this species from the soil and cleaning them it was 

 noticeable how very easily the white spongy outer cortex could be stripped 

 away from the central core. In the ultimate branches I found a tetrarch 

 condition of the stele. The four extended protoxylems and the four 

 compact groups of phloem which alternate with them are very distinct, 

 but the few large metaxylem elements, even in these small branches, are 

 continually changing their disposition. 



Mention has been made of the two kinds of underground stem of the 

 species L. ramulosum. Those which penetrate the soil most deeply are 

 brown in colour and smooth, being devoid of scale leaves. They are thicker 



than the white scaly rhizomes, 

 and their vascular cylinder is 

 proportionately larger. Fig. 12 

 shows the stele of the larger kind, 

 while the figure given in Part I 

 of these Studies (16, fig. 94) is 

 that of the smaller form The 

 cortical tissues differ consider- 

 ably from those of L. laterale. 

 There is an inner, thin-walled 

 zone, which in the large more 

 deeply growing rhizomes is re- 

 latively wide and contains much 

 starch, a median sclerenchy- 

 matous zone, and an outer, thin- 

 walled region in which there 

 are abundant air-spaces. The 

 vascular tissues correspond in 

 nature and arrangement to those 



Fig, 



12. — Lycojwdivm ramulosum. Transverse 



section of stele of deeply penetrating 



rhizome. X 137. 



j^ - 



of the other species in this 

 section of the genus. Practically surrounding the main vascular tissues 

 tliere is a ring of flattened and distorted cells. In sections of the mature 

 rhizome it is difficult to determine the exact nature of this ring, but from 

 a study of sections taken immediately behind the apex of the rhizome 

 it is clear that the original protoxylem has contributed to the greater 

 part of it. 



It is evident, then, that the vascular anatomy of the four New Zealand 

 species described above as belonging to the sections Inundata and Cernua 

 belongs to a common type which is best described as '' mixed," this 

 being seen best in L. cermaim. In all these species, although the habit 

 is plagiotropic, branching takes place all around the stem, so that no 

 directive tendency is present towards a dorsiventral disposition of the 

 vascular tissues as in the species of the Clavata section. The mixed nature 

 of the vascular tissues, however, is not merely the result of the all-round 

 branching ; it is present from the early seedling stages of the plant, and 

 goes along with certain characteristic features in the histology of the xylem 

 and protoxylem, and it is best regarded as part of the inherited constitu- 

 tion of this division of the genus. The only variation in the nature of the 

 vascular tissues is that in L. cernumn the phloem shows considerable 

 differentiation, this arising probably simply from the large size of the 



