T. Holm — Triadeniim Yirginicum (Z.) Rafin, 375 



there were twelve others, of the same shape, in the leptome. 

 No ducts were found in the pith. The structure of the tuber- 

 ous rhizome of J'riadenum is so different from that of Hyperi- 

 Giim Golycinum^ that a comparison seems unnecessary ; we 

 might only state that Yan Tieghem found four ducts in the 

 pith, corresponding with the four rows of leaves. 



The leaf. 



The aerial leaves are glabrous and very glaucous ; the struc- 

 ture is bifacial. Very characteristic is the marked difference 

 in the lumen of the epidermal cells, when we compare the 

 upper face with the lower, the cells of the upper being much 

 the larger. Stomata occur only on the lower face ; they are 

 surrounded by three to four cells and are sunk below the epi- 

 dermis ; the cuticle is smooth. 



The palisade tissue consists of but one layer and is quite 

 solid, in contrast to the open pneumatic tissue. The midrib is 

 prominent on the lower face, where it is supported by a coUen- 

 chymatic tissue, but without any stereomatic layers. The 

 translucid spots, so very characteristic of the order, are, also, 

 noticeable in Triadeiiiim^ but the dark spots are entirely want- 

 ing. Ducts like those described in the stem occur, also, in the 

 leaves and are of two kinds : Khombic (in cross-section), with 

 narrow secretory cells (D in fig. 4), were observed in the collen- 

 chypaa and close to the epidermis ; these, five in all, accompany 

 the midrib to about the middle of the leaf -blade, but not any 

 further. The other kind are, also, rhombic, but the lumen of 

 the secretory cells is much wider : these, five in all, are located 

 in the leptome (D in fig. 5) and may be followed throughout 

 the length of the midrib. 



So far as known, the stomata in the Hypericaoece are only 

 surrounded by two or three cells, thus Triadenxiin forms an 

 exception ; and the presence of ducts in the leaf seems to be 

 exceedingly rare, and usually restricted to the petiole alone. 

 The disposition of the ducts in the vegetative organs of Tria- 

 denum seems characteristic of the genus, when compared with 

 the other HypericacecB^ and four systems may be recognized : 



(1) The medullary, only observed in the stem above ground ; 

 (2) those of the cortex in the stolons, the stem and the leaf- 

 blade ; (3) those of the pericambium of the root ; (4) those of 

 the leptome in the root, the stem, the stolons and the leaf. 



There is, still, another species of Triadenwn in this country, 

 2\ petiolatum, and we regret to say that we have been unable 

 to secure fresh material of this for comparison. Judging from 

 the structure of the flower and the venation of the leaves, it 

 appears to belong to this genus, but, as is often the case, the 

 parts underground are but seldom preserved in herbarium-speci- 

 mens. We hope that future observers may study this species, and 



