BOTANICAL SUBJECTS. 165 



" or divide, but in a vague manner, and their new parts betir what 

 " are called root-hairs."* 



The stem, I would remark, does little more than this. Its 

 phyllotaxyf is probably due to the need of illumination of the 

 leaves in an erect stem. The rhizome of the seaweed and fern 

 has no phyllotaxis, because the leaves are all on one side and the 

 roots on the other. Roots give off leaf -buds just like the stem, 

 though, owing to the absence of light, phyllotactic regularity is not 

 developed. Stems, whether recumbent or erect, also give off roots. 

 The difference between roots and leaves therefore appears to be one 

 of ivords, respecting the medium in which each develops, and 

 respecting the function or division of labour which each assumes. 



Regularity in the disposition of underground nodes of course 

 is not needed, as it is in the above-ground nodes, for jjurposes of 

 full illumination. In the root, if it ever existed, phyllotaxis has 

 ceased to be inherited, as useless, while in the stem the phyllo- 

 tactic disposition is most useful, and continues to be inherited. 



The potato, Jerusalem artichoke, and many other plants, from 

 the points, which must of necessity be homologous with nodes, 

 give off not only underground stems or branches, but also roots 

 from those same nodes, just as the above-ground stems of orchids 

 and other plants do. So that, although the root may be func- 

 tionally different from the stem, it is morphologically the same 

 thing, that is, an off-shoot of a common placenta, which we call 

 node. In like manner, the stamen is functionally different from 

 the leaf, but morphologically it is the same thing, and under 

 certain circumstances is interchangeable with it. 



To begin by defining the stem as essentially one thing, and 

 the root essentially another, and then affirming that the one is not 

 the other, is much as if one defined the petal as a coloured organ 

 inside the calyx and the leaf as a green organ on the stem, and 

 then maintained that the petal is not a leaf ! By gi\'ing a thino- a 



* " These delicate root-hairs are the only organs which absorb the water, 

 containing small quantities of substances, such as salts of potash, lime, 

 nitrogen, phosphorus, &c. in solution, and they are utterly incapable of 

 perfoi-ming this Avork of absorption in the absence of oxygen." — Prof. H. 

 Marshall Ward {New Review, August 1891, p. 185). 



t Although rudimentary phj-llotaxis is apparent where there are no leaves, 

 but only nodes and internodes. The ridges of one intemode of the horsetail 

 alternate with those of another, and the internodes of Chara have often a 

 spiral twist, which may be the foundation of phyllotaxis. 



