430 



ANALOGIES — 



SHEATHS ON RADICLES. 



The Botanist who travels without the means of determining these 

 points, destroys half the value of his collections. 



December I6ih. — Yesterday was very raw and cloudy, to-day clear 

 as usual, towards 1 p. m. a strong north-east wind occurred for a 

 short time as usual, because once or twice before, it occurred after 

 threatening weather. 



Rationale. — It blows from the nearest snow to supply the rarified 

 air in the valley heated by the sun, even now tolerably powerful ; it 

 blows for some days so long as a vacuum is formed, and discontinues 

 when clouds again appear ; hardly so, as it before only blew for three 

 or four days, although several more elapsed before clouds re-appeared : 

 it may however be dependent on each fresh fall of snow in the hills. 



26th. — Cloudy morning, forenoon fine, clear and calm. 



Mosses are the analogues of Zoophytes ; these analogies are to be 

 looked for in the most striking and most constant parts of the orga- 

 nization of the divisions of nature. 



Marchantiaceae are the representatives of radiate animals, another 

 reason why Jungermanniaceae are to be separated from them. 



Hence, Radiata, = Marchantiacese. 

 ,, Zoophyta, = Musci. 



I am quite convinced that the true subordinate groups of Acoty- 

 ledones are far from being discovered. 



Are the sheaths found on certain radicles strictly confined to 

 monocotyledonous plants. There is this certain about them, that 

 they depend on the presence of vascular tissue, from which the radicles 

 or the divisions of each root originate : see young Hyacinth roots, 

 grown in water. 



Although the sheaths cannot exist without a positive cuticle, 

 their existence does not depend so much on its presence as on the 

 direction of the adhesive powers of its component parts : witness 

 certain forms of Marchantiacese, and the vaginate forms, as Azolla, 

 Lemna, etc. Also the sheath may not have adhesive powers at its apex to 

 prevent the escape of the radical at that point : witness Hyacinth roots ? 

 We may imagine a case in which the primary radicle may be with- 

 out a sheath, while its divisions shall have them, this depending on 

 the want of adhesion of the cuticle over the original one. 



The emerged and immersed leaves of plants are well worthy of exa- 

 mination, since Microphytum proves that stomata do not depend on 

 the presence of a cuticle as Brongniart supposes : their presence 

 is united with, or allied to an amount of density in the cellular tissue, 



