IS STIGMARIA A ROOT OR A RHIZOME? 363 



all this it seems reasonable to conclude that if not altogether nullified, 

 the evidence afforded by these bundles in favour of tlie view that the 

 appendages are rootlets is considerably weakened. Still, for the 

 present, it may be well not to insist upon this and to leave the 

 morphological nature of the appendages, so far as it is to be inter- 

 preted by structure, an open question. It hardly needs to be said 

 that even if they should eventually turn out to be rootlets, that of 

 itself would not be decisive of the nature of the axis. 



Summarising what has been advanced, it may be said then that 

 so far as external characters and internal anatomy are indications of 

 the morphological nature of the members of a plant, the facts seem to 

 point to the hypothesis that Stigmaria ficoides is a rhizome as the true 

 one. No one at this day disputes the fact referred to by Sir J. W. 

 Dawson and Professor Williamson, that Sigillaria and other Car- 

 boniferous plants were continued at the base of the stem into 

 StigmaricE. But this throws no light on the morphological nature of 

 the latter, although it may be conclusive enough as regards their 

 physiological functions. As the matter presents itself to a botanist, 

 it is for those who maintain the root hypothesis to explain how it 

 happens that all the characteristic root structures are absent, while 

 so many that are characteristic of stems are present. It may be 

 urged that, in Carboniferous times, the laws of plant morphology \vere 

 different from what they are to-day, and that we cannot interpret 

 palaeophytic structures in terms that are applicable to existing plants. 

 To this it may be replied that a generalisation so far-reaching as this 

 ought to be established on independent and indisputable evidence 

 before it is applied deductively to the solution of a controverted 

 question. As a matter of fact, palaeobotanists do not act upon any 

 such principle in dealing with the great majority of Carboniferous 

 plants, but, on the contrary, continually base their inferences as to 

 structure, affinities, modes of development, &c., on the assumption 

 that the same general laws are applicable to the whole Vegetable 

 Kingdom and to fossil as well as to recent forms. Another conten- 

 tion that may be advanced is that the various members of plants 

 were not so sharply differentiated in Carboniferous times as they are 

 to-day. This, at first sight, is a plausible contention, and deserves 

 candid and impartial consideration. But care must be taken to avoid 

 confusion in this matter between the plants of an earlier geological 

 epoch and plants of a less complex organisation. Among recent 

 plants, the distinction of root and shoot is well-known to be absent 

 from the lower forms, and to be restricted to vascular Cryptogams 

 and Spermaphytes. Hence there is no impropriety in saying that 

 in the lower forms the members of the plant body are not so sharply 

 differentiated as in higher types. But to apply this generally and 

 without qualification to Carboniferous plants is a much more ques- 

 tionable proceeding. Much, indeed, if not everything, depends upon 

 the type of plants that are under consideration. So far as I am aware, 



