LECT. VII.] SUBSTANCE OF STEMS, &C. 287 



1. The fleshy stem (C. carnosus) is that in 

 which the cellular substance, of which it is 

 composed, is turgid with fluids; and when 

 cut, presents a smooth, uniform moist surface, 

 similar to that of a young Cucumber when 

 transversely sliced. The common House-leek, 

 Sempervivum tectorum ; and most of the sea- 

 weeds, Algse, afford examples of the fleshy stem. 



2. The spongy stem (C. spongiosus) is com- 

 posed of a compressible, elastic, cellular sub- 

 stance, contained within an epidermis ; either 

 dry, the cells being filled with air only; or 

 moist, the cells being partially filled with fluid, 

 as in a sponge. The Mushroom tribe, Fungi ; 

 Indian Corn, Zea mays ; and Great Cat's-tail, 

 Typha latifolia, have spongy stems. 



3. The hollow stem (C.Jistulosus) is a suc- 

 culent or fleshy hollow cylinder, surrounded by 

 a circle of vessels and ligneous threads, imme- 

 diately under the epidermis ; and generally 

 lined with a dry white spongy layer of pith. 

 There are two varieties of the hollow stem. 



a. The uninterrupted (sine septis transver- 

 sisj; when the hollow, or cavity, extends 

 from the base to the apex of the stem, as in 

 the genus Coreopsis (Coreopsis). 



b. The interrupted (septis transversis inter- 

 tinctus) ; when either the longitudinal cavity 

 is divided, at regular distances, by parti- 



