422 CONSERVATIVE ORGANS. [LECT. VIII. 



one circle only round a pith, like those of the 

 second, I find that the fasciculi resemble those 

 in the Bryony, with the sap vessels, however, ar- 

 ranged in distinct divergent rays in each fasciculus. 

 The divergence, also, being on that circumference 

 of each fasciculus which is towards the centre of 

 the stem, and all the rays pointing more or less 

 to that centre, they are necessarily of very differ- 

 ent lengths: the longest rays generally containing 

 from six to ten vessels, whilst the number in the 

 shortest seldom exceeds two or three. Between 

 each ray we find the same condensed cellular septa 

 which Malpighi has described as existing in the 

 Endive. The sap vessels are all punctuated spirals; 

 but I have not been able to ascertain satisfactorily 

 the structure of the returning vessels, their deli- 

 cacy, transparency, and the milky nature of the 

 juice they convey rendering it impossible to make 

 out their characters distinctly, even under a mi- 

 croscope of the highest power. I have some rea- 

 sons for believing v that they are membranous and 

 cribriform. 



In concluding the view I have taken of this 

 division of herbaceous stems, it is necessary to 

 point out an exception to the general rule, that 

 all ligneous stems are necessarily perennials, and 

 all the herbaceous either annuals or biennials. In 

 the Thorn Apple, Datura stramonium, which is 

 an annual, generally described as herbaceous, 

 and which contains a large proportion of a very 



