IV. 



Is Stigmaria a Root or a Rhizome? 



IT is matter for congratulation that two such eminent authorities as 

 Sir J. W. Dawson and Professor WilHamson should have been 

 moved simultaneously to a publication of their views on Sigillaria 

 and Stigmaria (i). That this should have happened is of itself 

 sufficient to show that the subject is an important one, and that its 

 discussion at the present time is not inopportune. In again reverting 

 to it, I do not propose to take up all the numerous questions it 

 involves, and which, unfortunately, are not always clearly distin- 

 guished, but rather to deal briefly with one of them, viz., the 

 question as to the morphological nature of Stigmaria ficoides, apart 

 from its physiological functions. In doing so, no attempt will be 

 made to formulate a final and decisive opinion, but simply to indicate 

 the considerations that must be taken into account before the 

 question can be regarded as settled. It may be that to many 

 geologists and palaeontologists a purely morphological question will 

 possess but little interest, but to others, and especially to botanists, 

 there will be no need to apologise for its discussion. 



External Characters. — It has been pointed out again and again 

 that the external characters of Stigmaria ficoides were considered 

 by the older palaeobotanists as inconsistent with the view that it is a 

 root. So far as I know, no instance has yet been adduced in which a 

 root bears rootlets arranged in a quincuncial order, and in which the 

 rootlets become so regularly and so generally detached, leaving 

 behind such well-defined scars as those met with in Stigmaria ficoides. 

 Nor has any root hitherto been instanced in which the rootlets 

 approach so closely to the growing point of the axis as they do 

 in a specimen of Stigmaria described by Count Solms (2), where the 

 appendages grow smaller and shorter towards the apex, the distances 

 between them diminishing, while they become curved forward, and 

 close up like a bud over the growing tip. The same authority points 

 out that it is only as the appendages develop that they take up a 

 position at right angles to the axis, so that they show the phenomena 

 of epinasty and hyponasty like ordinary foliage leaves, phenomena 

 which up to now have been unheard of in the case of rootlets. 



In his communication to this Journal (3), Sir J. W. Dawson 

 states that Stigmaria " grew in the underclays or fossil soils, and that 



