T. Holm — North American Terrestrial Orchidece. 205 



And as already described by Irmisch (1. c.) as characteristic of 

 the European S. autumnalis Rich., the cells of e^dermis show 

 the same spiral thickening as we find in the velamen of the 

 epiphytic genera, besides that a similar thickening of the cell- 

 wall is, also, to be observed in the hypoderm of S. cinnabarina 

 and Asagrcei. The cortex is thin-walled and the cells of the 

 innermost layers are very often stretched radially ; the number 

 of layers varies somewhat, but is usually about 15, and the 

 contents consist mainly of starch, except in the last two 

 species, where only hyphse were observed ; it seems altogether 

 as if the function of these fleshy roots of Spiranthes is to store 

 starch and not water, although the nature of the habitat might 

 suggest that water-reservoirs would be needed. In S. simplex 

 and S. prcecox no hyphse were observed in any of the tissues, 

 but in the other species the roots proved to be real mycorhizce. 

 As to the innermost layer of the cortex, the endodermis, this 

 seems to be invariably thin-walled in the species examined and 

 shows the Casparyan spots very plainly. The pericambium is 

 represented by only one layer ; it is very irregularly interrupted 

 by the proto-hadrome vessels in S. gracilis, S. simplex and S. 

 Romanzoffiana, but in certain roots of the last species it 

 occurred, also, as a continuous ring, the proto-hadrome being 

 located inside. In 8. prcecox the pericambium was found to 

 be continuous near the base of the root, but interrupted near 

 the apex of same. The rays of the hadrome, from 12 to about 

 20, are very short in all the species and contain but a few 

 vessels, alternating with similarly very small groups of lep- 

 tome, while the greater portion of the central-cylinder is occu- 

 pied by a large mass of thin-walled parenchyma, a true pith. 



Type C. 



The roots of this type are more or less tuberous and contain 

 several cylinders of leptome and hadrome. 



Orchis spectabilis L. 



If we examine the tuberous root below the hibernating bud, 

 we notice the following structure. Epidermis is thin-walled 

 and there are many root-hairs. Underneath the epidermis is a 

 thin-walled cortex of about 8 layers containing starch and 

 hyphse, and which borders on 2 mestome-cylinders separated 

 from each other by a few layers of parenchyma, which shows 

 the same structure and contents (starch) as the peripheral cor- 

 tex. Each mestome-cyhnder is surrounded by a thin-walled 

 endodermis, inside of which is a pericambium, which is broken 

 by the proto-hadrome vessels in several places. The hadrome 

 constitutes about 12 irregular and very short rays, which alter- 



