396 SYDNEY H. VINES. 



siders them to be elements of the xylem. It seems probable 

 that the view which Schwendener takes of their morpho- 

 logical value is the correct one, and, if this be so, all that 

 has just been said of the bast cells applies equally to these. 



With regard to Dicotyledons and Gymnosperms we have 

 seen (fig. 2) that the bast cells, which we no longer consider 

 as essential constituents of the phloem, most frequently invest 

 the outer surface of the soft blast (true phloem) as a support- 

 ing sheath, but, as in the Monocotyledons, they bear no con- 

 stant relation to the other elements of the bundles. We find 

 them alternating with layers of soft bast (Tilia, Juniperus, 

 fig. 5), Ave find them lying internally to the xylem (Cucurbita, 

 Bryonia, Fig. 6), and we find them forming independent 

 bands in Rhipsalidese.^ Schwendener^ goes on to point 

 out that there is a similarity, amounting almost to iden- 

 tity, between the structure of the bast cells and that 

 of the woody fibres (libriform of Sanio'^) ; and he regards 

 these structures as being intimately related. He con- 

 cludes that, as in Monocotyledons so in Dicotyledons, the 

 prosenchymatous cells are arranged in the tissues in obe- 

 dience to mechanical and not to morphological laws. 



As the result of his investigations, Schwendener is led to 

 regard all the prosenchymatous cells of a plant, whether oc- 

 curring in the ground tissue, in the phloem, or in the xylem, 

 as being specifically mechanical elements, and as forming 

 parts of the hard skeleton of the plant, arranged in accordance 

 with purely mechanical laws. For the entire system made 

 up of these cells he proposes the name " Stereom," each one 

 of the cells being termed a " stereide," but these cells are 

 still called bast cells, even by himself. 



These views have been, on the whole, accepted as well 

 founded by subsequent observers. Russow^ admits that the 

 view which regards the bast cells (sclerenchyma), which 

 more or less invest the periphery of the bundles, as belonging, 

 not to the bundles, but to the ground tissue, is proved as 

 well by morphological and physiological as by phylogenetic 

 evidence, for he thinks it probable that the function of sup- 

 port which, in the Archegoniata, is assigned to elements of 

 the ground tissue may, in course of time, have been trans- 

 ferred, by gradual adaptation, to the elements of the 

 bundles. 



' Vochting, " Beit, zur Morph. u. Auat. der Rhipsalideen," ' Jhrb. f. Wiss. 

 Bot.,' is, p. 475, 1873-74. 

 - Loc. cit., p. 6. 

 3 ' Bot.. Zeitung; 1864-65. 

 •* ' Betracbtungen,' p. 12. 



