144 Vegetable Physiology. 



surface of the water : the petioles are inserted exactly in th 

 centre, and are very long and slender. The flowers are p Ur . 

 pie, on similar stalks, and the whole under surface of the 

 leaves, together with the stem, is covered with a white slime 

 The order Nelumbiace^e comprises only one genus, a species 

 of which, Nelumbium luteum, or Water Chinquapin, is a fine 

 plant, growing in the lakes of the South and West, but some- 

 times met with in some parts of New England. The nuts are 

 roasted and eaten, or are ground into a kind of flour. 



VEGETABLE PHYSIOLOGY. 



NUMBER FIVX. 



Form and Stuctube op the Stem. — The stem may be 

 defined as that part of a plant, which, proceeding from the 

 root, either extends under ground, or ascends into the air, and 

 supports the leaves and flowers, and its chief office appears to 

 be to elevate these into the most favorable position for receiving 

 the influence of heat, light, and air, on which their due action 

 depends. All flowering plants are furnished with stems, though 

 in some instances the stem does not rise above the ground, or 

 is so short as to appear wanting. In annual plants the stem is 

 generally herbaceous, consisting mostly of soft cellular tissue, 

 but containing some woody fibre and spiral vessels, which are 

 traceable in the stalks of the leaves, and in the strings of such 

 vegetables as the Asparagus. In longer lived plants, however, 

 the stem becomes more and more solid, by the formation, each 

 year, of new bundles of this fibre, which, in time, nearly displa- 

 ces the soft tissue. 



We have already seen that the stems of flowering plants 

 are not all formed in the same way, but that there are two 

 different modes in which the woody matter is arranged : that 

 one set of plants increases by the deposition of this matter in 

 the interior of their stems, and another by its deposition on the 

 exterior ; that the former are called Endogens, and the latter 

 Exogens ; and that the Exogenous stem consists of pith, wood, 



