STEM. 11 



54. The development of the stem is in general cylin- 

 drical, and its direction perpendicular, and these always 

 exist in the earliest stages of its growth. Sometimes, 

 however, the development becomes spheroidal or glo- 

 bose, or the direction horizontal, and these take place 

 under or near the surface of the ground. 



55. From the more or less spheroidal development of 

 the base of a stem, we have produced the cormus and 

 the tuber. 



56. The cormus seen in the Colchicum and Crocus, is 

 an enlarged base of their stem, containing along with 

 much cellular, both fibrous and vascular tissue, and from 

 which, in many cases, the new plant arises in the spring 

 of the year. 



57. The tuber is seen, for instance, in the Potatoe, 

 which is a development of cellular tissue increased to a 

 very great extent in the lower part of the stem, and 

 which possesses buds or eyes capable of giving rise to 

 new individuals. 



58. The cormus belongs more especially to monoco- 

 tyledonous plants. 



59. From the more or less modified direction of a 

 stem under or near the surface of the ground, we have 

 produced the caulis repens and its modifications, and the 

 caulis procumbens and its modifications. 



60. The caulis repens, or creeping stem, is a stem 

 running along beneath the surface of the ground, and 

 sending out rootlets and plants at certain intervals, 

 as in Couch-grass, or else becomes very much thick- 

 ened, and lies upon the surface of the earth, when it 

 constitutes a rhizoma, as in the Sweet flag, (acorus 

 calamus.} 



61. The caulis procumbens, or lying stem, has various 

 modifications ; the whole stem or plant sometimes lies 

 along the surface of the ground; it is then simply 

 procumbent : sometimes the end of the stem produces 

 roots arid a young plant, as in the strawberry ; it is 

 then sarmentose, and the trailing stem is a runner, &c. 



62. Independent of the cormus and tubers, there are 



