T. Holm — North American Terrestrial Orchidece. 197 



Art. XX Y. — The root-structure of Worth American terres- 

 trial Orchidea3 ; by Theo. Holm. (With figures in the 

 text.) * 



Few orders have offered a larger number of interesting data 

 in the various phases of the life-history of plants than the 

 Orchidece. By their manifold structures, readily perceivable 

 among their various biological types, they have for years 

 attracted considerable attention and furnished ample material 

 to writers on morphological and anatomical botany. It is 

 quite natural that the epiphytic species have received a more 

 general treatment than the terrestrial, on account of their 

 unquestionable prominence in floral and vegetative characters, 

 besides that their cultivation being less difficult has made them 

 more accessible to study than the others. Among the terres- 

 trial species very few have been studied from a general point 

 of view except old-world species, but several of these have, 

 nevertheless, served as the very basis of such magnificent con- 

 tributions to science as those of Irmisch. While, thus, our 

 native, terrestrial Orchideai are very little known from a mor- 

 phological and anatomical point of view, the following notes 

 on their root-structure are offered as a small contribution to 

 the knowledge of these interesting plants, with the intention 

 to add some further observations in a subsequent paper, which 

 we have made upon the other organs. 



As a general result of these observations we might state 

 here, that it seems to be a rule that a tuberous rhizome is 

 only provided with slender roots as is the case with Arethusa, 

 Calypso, Bletia, Tiptdaria, Ajplectrum, etc., while species 

 with slender rhizome may possess tuberous roots, as for instance : 

 Orchis sjpectabilis, Platanthera, Spiranthes, etc., or the roots 

 may be equally slender, as in O^j/ripedium, Goodyera and 

 certain species of Pogonia: verticillata, ophioglossoides and 

 divaricata. — We might, also, call attention to the fact, that 

 the development of such varied structures of roots and rhi- 

 zomes does not seem to be dependent upon any special nature 

 of environment ; on the contrary, species with tuberous 

 rhizomes may occur in open bogs as well as in deep, shaded 

 woods ; and species with tuberous or slender roots may be 

 found in bogs, ravines, in dry fields or in clearings in thickets. 

 In this particular respect the plants themselves seem to 

 possess a very pronounced individuality, and are difficult to 

 classify as meso-, hydro- or xero-phytes. It appears even to 

 be ratner uncertain whether some of these species are to be 

 considered as auto-phytes or hemisapro-phytes. — And when we 

 consider the general structure of the roots alone, it seems quite 



Am. Jour. Sci.— Fourth Series, Yol. XYIII, No. 105.— September, 1904 

 14 



