374 T. Hohn — Triademtm. Yirginicum (Z.) Rafin. 



four secretory cells ; the hadrome consists of many vessels with 

 a few strata of thick-walled conjunctive tissue. 



The secondary roots developed upon the rhizome are quite 

 thick and show the same collapsing of the cortical parenchyma ; 

 the pericambium has commenced to divide itself tangentially 

 with the large ducts still persisting, and, moreover, similar ducts 

 are, also, observable in the leptome ; a small cambium is devel- 

 oped and the hadrome occupies the greater portion of the cen- 

 tral cylinder. In other words, these secondary roots show the 

 structure of the perennial type. Van Tieghem, who studied 

 the root of Hypericicm calycinu7n (evidently " lateral roots "), 

 observed two ducts in the pericambium, one on each side of 

 the leptome, but none in the leptome itself. 



The aerial stem. 



This is glabrous and cylindrical with a thick-walled epi- 

 dermis, which covers some five or six layers of cortical paren- 

 chyma with distinct intercellular spaces, but without lacunes ; 

 there is a thin-walled endodermis surrounding the leptome, 

 cambium and hadrome, and the innermost part of the central 

 cylinder is occupied by a pith, which soon becomes hollow. 

 ^o stereome or hypoderm was observed. Two kinds of ducts 

 occur in the stem ; some with the four secretory cells very nar- 

 row (fig. 6), which traverse the cortex close to the epidermis, 

 and of which there may be until twenty, and others with wide 

 secretory cells (fig. 7) which are developed in the leptome and 

 which are very numerous. In the uppermost portion of the 

 stem, where the pith was unbroken, a single duct, rhombic in 

 cross-section, was observed in the center. The occurrence and 

 arrangement of the ducts in the stem seems very variable, and 

 has been described by Yan Tieghem in species of Hypericum, 

 Tridesmis, Haronga, etc., but they do not seem to be frequent. 



When present in the pith the ducts are said to occur to the 

 number of four, evidently corresponding with the four angles 

 of the stem ; the single and central duct observed in the pith 

 of Triademom seems thus to correspond with the circular out- 

 line of the stem. 



The rhizome. 

 The stolons, slender and tuberous alike, have several layers 

 of cork underneath the epidermis ; the cortex forms a broad, 

 but very open, tissue, and there is an endodermis of the same 

 structure as observed in the above-ground stem. The leptome 

 and hadrome enclose a central pith of rather small cells. Ducts 

 are quite numerous in the internodes and we counted about 

 forty in the cortex near the periphery, which were round, not 

 rhombic, in transverse section (D in figure 8) ; besides these 



