FROM THE LOWER COAL-MEASURES. 97 



whose divisions the whole of the root-tissues are ultimately 

 built up * Elaborate details are given by Van Tieghem of the 

 mode of development, but there is nothing in our specimen to 

 indicate that its roots have originated in the way he so 

 carefully describes. 



As regards Carboniferous plants, Psaronius is perhaps the 

 best known example of a stem with roots running in the cortical 

 tissues. From what is known of its structure t, it is usually 

 regarded as the stem of a Fern, which probably attained arbo- 

 rescent proportions. According to the best authorities, the 

 parenchymatous cortex varies in thickness, and is traversed by 

 numerous roots running nearly perpendicularly downwards. It 

 may be said therefore to bear some resemblance to our speci- 

 men. But in Psaronius the vascular bundles of the stem are 

 not collateral, and the roots usually have a hexarch or pentarch 

 vascular strand and a cortex which is uniformly and perfectly 

 normal when compared with that of recent plants. On the 

 other hand, a3 in some of the roots of our specimen, the outer 

 limit of this cortex is not quite sharp, and appears to stand in 

 direct union with the stem-tissue in which it lies. How this 

 last feature has come about has not yet been determined. Ac- 

 cording to some authorities it is produced by a growing together 

 of the stem and root tissues ; but Stenzel % is of opinion that it 

 marks an early stage of root-development, to be followed later 

 by a complete separation from the parent tissue. As is pointed 

 out by Solms-Laubach, this implies a mode of development very 

 different from anything we know to occur in recent Ferns, but 

 it is not without interest in relation to the plant we are dealing 

 with. 



It would seem, then, that neither among recent plants nor 

 among the plants of the Coal-Measures hitherto described is 

 there anything which is strictly comparable to this part of the 



* Van Tieghem, "Recherches comparative sur Torigine des merobres cndo- 

 genes duns les plantes vasculaires," Ann. d. Sci. nat., Botanique, scrie Tii. 

 tome viii. 1888, pp. 553, 561. Ooebel, loc. cit. p. 258. 



t Russow, ' Betrachtungen uber das Leitbundel- und Grundgewebe,' p. 51. 

 " Iras-Laubach, loc. cit. p. 174 (Engl. ed. p. 171). Schenk, loc. cit. p. 48. 



Williamson, 'Organization of the Fossil Plants of the Coal -Measures. 

 Parts vii., xii. 



X This statement is made on the authority of Solms-Laubach, he. cit. 

 p. 175. 



