T. Holm — North American Terrestrial Orchidece. 201 



tral group of slightly thickened parenchyma. The leptome 

 occurs as small, roundish groups in transverse section. Hyphad 

 were found in the cortex of C. multiflorus arfff C. pidchellus, 

 hut none in the third species. 



In the following genera of this same type the roots are quite 

 slender, but possess in contradistinction to those described in 

 the preceding, a well developed central parenchyma, which 

 evidently represents a true pith, homologous with the pith of 

 the stem. 



Habenaria repens Nutt. 



This species is a native of very damp places, and when grow- 

 ing in water the very long roots produce root-shoots. A thin- 

 walled epidermis with few hairs and a hypoderm surround a 

 cortex of about 20 layers of thin-walled cells, of which the 

 outermost 4 constitute a compact and persisting tissue, while 

 the interior 16 are traversed by numerous lacunes from the 

 very wide intercellular spaces ; only a little starch, but many 

 bundles of raphides were observed in the cortex, besides 

 hyphee in the peripheral strata. The cortical parenchyma is, 

 thus, very open, and in several roots, in the entire length of 

 these, a well defined duct was furthermore observed, sur- 

 rounded by a sheath of very small, thin-walled cells ; neither 

 liquid or solid contents were observed in this duct, and its func- 

 tion may evidently be for osmotic exchange of gases. 



The endodermis and the continuous pericambium are both 

 thin-walled. In regard to the hadrome and leptome, the former 

 does not occur in rays, but merely as small groups, from 6 to 

 15, each consisting of a few, 2 to 5, mostly wide vessels, which 

 to a more or less extent alternate with the equally small groups 

 of leptome. The arrangement of the hadrome in proportion 

 to the leptome is somewhat irregular, and we observed several 

 cases where the leptome was really located in front of the 

 hadrome, thus imitating the radial position of these same ele- 

 ments in the stem ; in other cases the vessels were on each side 

 surrounded by a group of leptome with the two proto-leptome 

 cells very distinct (fig. 1), as in mestome-bundles of the hadro- 

 centric type, and this position was frequently observed in 

 H. repens. The larger portion of the central cylinder consists 

 of a thin-walled pith with deposits of starch. 



Arethusa bulbosa L. 



The epidermis is thin-walled and densely covered with long 

 hairs ; there is, also, an hypoderm, but not easily distinguish- 

 able from the cortex. The latter consists of about 6 compact 

 layers with many hyphae, but without starch. Endodermis and 

 the continuous pericambium are both thin-walled and surround 



