36 DIMORPHISM OF RESTIACE.E. 



" Ut vero pistillnm credamus esse rudimentnm sexti aniii 

 foliorum, eo inducimur, qiiod iiou sine singulare volniDtate vidimus 

 qnomodo flores pleni Cardni Juctcrojjhi/Ui et tatarici, in quibns flores 

 majores evasere, seminum Pappo dilatato in foliola angusta laci- 

 niata, Corollis majoribus, crassioribus, instar foliorum, viiidibus et 

 serratis, stamimun filamentis castratis, sed stijlo, quod singulare, 

 enato in duo foliola viridia serrato ciliata, ad similitudinem bracte- 

 arum." (Linn. ' Prolepsis Plantarum,' 1760, ' Amoenitates Acade- 

 micse,' yi. p. 338.) 



NOTE ON THE DIMOKPHISM OF EESTIACE^. 



By Maxwell T. Masters, M.D., F.E.S. 



(T.^. 194, II.) 



Although the genera of Piestiacea; are in general easily recog- 

 nisable wlien the female plants are at hand, yet it is no easy matter 

 to discriminate the species of the larger genera one from the other. 

 Often, too, there is a greater difference in outward appearance 

 between the male and female plants of the same species than 

 there is between plants of widely different generic structure. The 

 male plants of different species, and, in some cases, of different 

 genera are so singularly alike that it becomes a matter of difficulty, 

 sometimes even of impossibility, with the material at command, to 

 determine with anj^thing like confidence even the genus to which a 

 particular male x)lant belongs. This being the case, the botanist 

 who occupies himself with these plants is glad to avail himself of 

 any character, however intrinsically unimportant it may seem, 

 which may enable him to discriminate between the sj)ecies or 

 groups of species. The characters afforded by the persistence or 

 caducity of the sheaths which encircle the stem at more or less 

 distant intervals afford useful generic distinctions, while, in the 

 genus Piestio itself, two generally well-defined groups may be con- 

 stituted, according as the leaf-sheaths or vaginae are loosely or 

 tightly wrapped around the stems. In ascertaining this point 

 only those sheaths should be considered which have no branch or 

 shoot in their axils, because, of course, the presence of such a 

 shoot would involve a more or less loose fit on the part of the 

 investing sheaths. Of less importance for specific distinction is 

 the iDresence of stems of two forms — the one relatively unbranched, 

 erect, leafless except as to the sheaths, and usually bearing the 

 inflorescence ; the other comparatively shorter, much and intri- 

 cately branched, the ultimate branchlets being fine, needle-like, 

 often more or less curved, and bearing a large number of small 

 leaves, provided not only with the vaginal j)ortioii but also with 

 linear needle-lilie curved laminfB. Some species appear never, or 

 rarely, to produce sterile branches of this character ; others con- 

 stantly produce dimorphic branches. In this latter case, the 

 character of the sheaths is, except in one instance now to be 

 noted, invariable. The exceptional case is afforded by Hesfio 



