T. Holm — Triademmu Yirginiciim (Z.) Rafin. 373 



marked deviation from the genus Hypericum^ the organs 

 above ground are of no less importance. We need only refer 

 to the floral structure, as already indicated by Rafinesque. But 

 besides this the leaves show a character by which they may be 

 readily distinguished from those of broad-leaved species of 

 Hypericum^ not including Androscemiim^ which is evidently a 

 distinct genus ; this character consists in the venation : the 

 veins in Triadenxiin being very prominent on the lower face 

 of the blade, and the secondaries being more numerous, but 

 shorter and proceeding from the midvein under an angle that 

 is much broader than is observable in the leaves of Hypericum. 

 In the latter the secondaries proceed, as a rule, from below the 

 middle of the midvein, while in Triadenum they are notice- 

 able almost to the apex of the blade. These are the points 

 which we observed in the external structure of our plant, and 

 which ought to be mentioned in the diagnosis, whether it be 

 accepted as a genus or not. 



The observation of these characters induced the writer to 

 extend the study to the internal structure, and to compare this 

 with what is known, so far, about the general anatomy of the 

 order. Moreover, Triademim has not hitherto been exam- 

 ined from this point of view, and, as will be seen in the follow- 

 ing, it possesses certain structural peculiarities which, together 

 with the morphological, seem to entitle it to generic rank. 

 The anatomy of the vegetative organs is as follows : 



The root. 

 On the almost capillary, lateral roots developed upon the 

 main one, hairs occur in abundance ; there is a narrow cortical 

 parenchyma, which is quite solid, and of which the cells are 

 arranged radially towards the thin-walled endodermis, in which 

 the spots named after Caspary are plainly visible. The peri- 

 cambium consists of two layers outside the leptome, but of 

 only one outside the hadrome. The root is diarchic with, in 

 all, four vessels in two groups separated from each other by a 

 few strata of thin-walled conjunctive tissue, and alternating 

 with two groups of leptome. Ducts of rhombic cross-section 

 are developed in the pericambium, one outside each of the two 

 groups of leptome. Roots that are slightly thicker show the 

 same structure, but are triarchic. But if we examine one of 

 the thicker, lateral roots, we notice the structure to be some- 

 what different ; the cortex, consisting of seven layers, shows a 

 tangential collapsing of the innermost five ; the endodermis 

 shows a number of radial divisions, while the pericambium 

 exhibits the same structure as in the thinner roots, though with 

 a larger number of ducts outside the broad groups of leptome ; 

 these ducts are, also, rhombic in transverse section and have 



