SPHENOPHYLLEAE. 



and plausible ; but as there can be no certainty in the matter without a 

 knowledge of the development, we do not gain much by these explanations. 



The wood-strand goes through the nodes, as Renault showed, without 

 perceptible change. Here a leaf-trace of a single strand emerges at once 

 and attaches itself to each of the initial bundles. The traces which thus 

 arise in pairs at the corners (Fig. 48, 4) pass through the rind in a horizontal 

 course and with slight divergence, and usually branch dichotomously while 

 still inside it. If now we may assume that a single bundle enters the leaf 

 in all the forms, as Schenk has shown to be the case in one of them (see 

 above on p. 343), the number of the leaves may be concluded directly from 

 the structure of the transverse section of the node. The node figured by 

 Renault 1 and given here (Fig. 48, 4) must thus have borne twelve leaves, 

 those represented by the same author in a previous publication 2 must have 

 had eighteen. But the difference in their outline shows that these sections 

 belong to different species, in which there might very well be distinctions in 

 this direction, such as are in fact alleged by Grand' Eury 3 . One thing 

 however is by this means absolutely proved, as Renault 4 has pointed out, 

 namely, that the leaves in consecutive whorls were superposed. And if this 

 can be directly shown in Trizygia speciosa, and its leaves are moreover 

 combined in pairs, it appears to me that we have no slight proof that the 

 plant belongs to the present group. The unequal distribution of the leaves 

 round the periphery of the nodes will be accompanied, as might perhaps be 

 expected, by bilateral symmetry in the structure of the central strand. 



Pieces of young stems showing only the primary structure are however 

 rare; specimens with secondary wood more or less developed are much 

 more common. Van Tieghem's 5 charge against Renault, that he has 

 mistaken the nature of this wood, seems to me, as so put, to be unfounded; 

 Renault has described it correctly, only he has preferred to use a neutral ex- 

 pression which does not prejudge anything, and to call it a 'sheath of 

 punctate tubes.' The woody body in question consists then chiefly of broad 

 tracheal elements, having the form of four-sided prisms with a regularly 

 square transverse section, and with the vertical and radial angles replaced by 

 narrow planes of truncation. On the tangential section therefore they are 

 seen as continuous vessel-like tubes, in the radial direction they have the 

 appearance of being made up of many members set one on another, and 

 looking like the component members of normal vessels (Fig. 48, 3). Whether 

 they are really of this kind has not yet been ascertained ; there is no 

 appearance of transversal parting walls, but these might have perished by 

 maceration before petrifaction. On the other hand, no pointed extremities 

 pushed in between one another, such as are usual in tracheides, have ever 



1 Renault (20), t. 7, f. 3. a Renault (16), t. 4, ff. 3, 4, and t. i , f. 5. 3 Grand' Eury (1), p. 51. 

 * Renault (2), vol. iv, Introd. p. 29. 4 van Tieghem (3), p. 173. 



