OF VEGETABLE TISSUE. 13 



soft state, no juice is ever seen to issue from the 

 orifice of a spiral vessel; and though, as the 

 lymph is found to ascend in the stalks of mosses, 

 &c. which do not possess these vessels, we may 

 probably conclude that they are not requisite to 

 the transmission of fluid, though occasionally so 

 employed. 



The Laticiferous Tissue consists of very de- 

 licate and anastomosing tubes, principally oc- 

 curring in the young bark, and on the under 

 sides of young leaves. They convey the fluid 

 called Latex, or proper juice ; which constitutes 

 the nourishment of the young organs, and in 

 which a curious oscillation of globules is visible 

 in the bright sunshine, with a powerful micros- 

 cope.* 



seq. The line of demarcation between the form of the 

 true spiral vessel, and some of the ducts, is sometimes 

 difficult to find ; in some vessels there are ohscure traces 

 of spiral form, interrupted in places, and covered by 

 membrane. " In Ferns, (which have no true spiral 

 vessels) we find Ducts, which very closely approach the 

 spiral vessel in character, having an unbroken coil of 

 spiral fibre throughout their whole extent ; but besides 

 the important difference that these ducts are long, con- 

 tinuous tubes, they are further distinguished by the 

 brittleness of the spire, which snaps when we attempt 

 to unrol it." Ibid. 82. 



* For a further account of this and other local circu- 

 lations, see Appendix (A). 



