T. Holm — North American Terrestrial Orchidece. 209 



between the lines 4 and 10. Underneath or better " behind " 

 the bud, as the figure shows, is a cylindrical body between the 

 lines 4 and 10, which cannot possibly be defined as represent- 

 ing a stem (stolon) or a root alone, but appears to be a con- 

 crescence of both ; the result of our anatomical investigation 

 is in favor of this explanation. 



In our figure 2, the dotted lines indicate the places where 

 the most important sections have been laid, and the general 

 structure of the rhizome may be briefly described as follows : 

 At its very base (st.) the stolon exhibits a structure like that 

 of a typical rhizome with a distinct central-cylinder, surrounded 

 by an endodermis, and with all the minor characters of a stem- 

 portion. But if we examine a section of this same stolon 

 taken a little further down, by the line 2 for instance, the 

 structure is somewhat different, since we observe there two addi- 

 tional, but very small, mestome-cylinders, which are located 

 underneath the central- cylinder ; each of these two mestome- 

 cylinders possess an endodermis and a pericambium (End. and 

 P. in fig. 3) and they represent two roots or at least two 

 primordia of such. By continuing our examination of the 

 same rhizome, we observe in section 3 not less than five small 

 mestome-cylinders besides the central, of exactly the same 

 structure as the two described above, and these are very reg- 

 ularly arranged in an arch which is parallel with the lower 

 face of the stolon. At the same time the epidermal structure 

 has become changed, thus the cells on the lower face of the 

 stolon are more or less extended into papillge and have attained 

 a darker color in contrast to the epidermis of the upper face, 

 which has retained the typical structure of a stem-epidermis. 

 In other words, the stolon has started to become dorsiventral 

 with the development of roots on its ventral face, accom- 

 panied by the characteristic epidermal structure. 



In following the structure further down to section 4, the 

 large cylinder, formerly central, has become moved nearer the 

 dorsal face of the stolon, and the number of small mestome- 

 cylinders has increased to ten, arranged in two arches parallel 

 with and located near the ventral face. The distinction in 

 regard to the epidermal structure is still more pronounced in 

 this section, and the dorsal epidermis occupies a zone that is 

 much narrower than the ventral. A gradual increase in the 

 number of mestome-cylinders takes place further down, and 

 thirteen were noticed in the sections taken by the lines 5 and 

 6 ; furthermore, by 6, the large mestome-cylinder of the stolon 

 is not only still nearer the dorsal face than we observed before, 

 but its pith has become reduced quite considerably in width. 

 And in regard to the bud, the outermost leaf shows here (at 6) 

 a distinct swelling, caused by a cavity at its base. The broad- 



