Foliar Ray in the Wood of the Dicotyledons. 657 



may be seen five depressed segments. In this twig the foliar ray has 

 disappeared except from the immediate vicinity of the leaf-traces. The 

 normal twig possesses a circular outline, and the foliar ray is not con- 

 spicuously developed at the node. This recurrence of depressed segments 

 in vigorous shoots of Castanea indicates that five pairs of approximated 

 lateral leaf-trace rays existed formerly in the mature twigs of these plants, 

 and have disappeared except from the nodes of very vigorous stems. In 

 Castanopsis indications of depressed segments which were once a well- 

 developed feature of the plant persist in the normal mature twigs. A cross- 

 section of the node of Castanopsis hystrix is illustrated in PI. LXIII, Fig. 16. 

 Two segments (y] are more strongly depressed upon the upper side of the 

 photomicrograph, due to the fact that the rays related to the lateral leaf- 

 traces are persistent at the node. Owing to the phyllotaxy of the plant 

 the three remaining segments (x) are less strongly depressed. Fig. 14 

 shows a cross-section of the mature stem of Castanopsis indica. In this 

 species the five depressed segments are more persistent between the nodes, 

 and indicate that the reduction of the foliar ray is less complete in this 

 plant than in the preceding species. In Fig. 13 may be seen the cross- 

 section of a mature twig of Castanopsis tribuloides, a plant whose structure 

 resembles that of Querciis, since the lateral leaf-trace rays are strongly 

 developed in the wood of small twigs. A careful study of the life-history of 

 the plant reveals the fact that the aggregated rays are disappearing in many 

 portions of the root and stem. In PL LXII, Figs, n and 13 are illustrated 

 the remains of aggregate rays which were once strongly developed by the 

 cambium to maintain the proper proportion of ray tissue in the widening 

 stem and root. These facts, considered in connexion with evidence afforded 

 by the recapitulation of primitive characters which occur in vigorous 

 mature ramifications, nodes, and traumatic regions, point conclusively to 

 the reduction of foliar rays in certain Fagales, and indicate that Castanopsis 

 and Castanea are reduced members of the oak family, just as Alnns mollis, 

 A. acuminata, and A. yasha must be considered reduced species of the 

 genus Alnus. 



The uniseriate rayed species of the Salicales (9) and Sapindales (10) 

 have been studied by Miss Holden, and have been found to represent 

 a reduced condition where complex ray structures have been lost in a 

 reversion to the primitive uniseriate type, but among the higher families 

 of Dicotyledonous plants the uniseriate condition has resulted largely from 

 the reduction of foliar rays of the diffused type rather than of the 

 aggregate or compound types. 



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