PITH. 67 



Umbelliferous plants it forms a fine delicate lining, re- 

 markable in some cases for its brilliancy, and in many 

 of the grasses it presents a similar appearance. But in 

 the Zgzania or wild Rice, one of the largest grasses in 

 New-England, it forms in addition to this lining, distant 

 partitions which interrupt the cavity of the stem. — 

 When young the pith is usually green, becoming of a 

 snowy whiteness when old, though in a few cases it 

 becomes yellow or brown. 



Its texture is precisely similar to that of the cellular 

 integument, being composed of cells which are seen to 

 the best advantage in the centre, for there they are 

 least compressed by the surrounding layers of wood. 

 These cells, which are unusually large in the Elder, 

 are filled with fluids when young, but in old branches 

 the fluids are gone and the empty cells only remain. 



The pith is sometimes interspersed with fibres of a 

 very different texture. They occur in the old stems 

 of the Elder, and are still more conspicuous in the stalk 

 of the Indian Corn. In the former case, they are dis- 

 tinguished by their peculiar colour from the pith in 

 which they are imbedded, and the formation of these 

 fibres has been regarded as the commencement of the 

 process, by which the pith is converted into perfect 

 wood. 



Of its uses in the economy of vegetation, but little is 

 known. Its structure being similar to that of the cel- 

 lular tissue, it is probably subservient to the same pur- 

 poses, though some writers have assigned to it more 

 important functions. Among them was Linnaeus, by 

 whom it was regarded as the source of nutriment, and 

 the seat of vegetable life. Others, and among them is 

 Mr. Knight, regard it as a reservoir of moisture, to 

 supply the leaves when exhausted by excessive exha- 



