alttumen. 



ON THE STRUCTURE AND CLASSIFICATION Ol* SEEDS. 



of great use in showing the formation and habit of a seed, 

 and teach more (if well studied) than any other: the 4th 

 and 5th classes are large enough to be dissected with the 

 usual instruments. But for the diminutive seeds larger 

 powers are required, as the powdered lichens, fungi, mosses 

 of the smallest kind, &c. It is best to keep these till 

 very ripe, then place the seeds in the several sliders of the 

 solar or double iwicroscope, and you will always find two 

 or three opened sufficiently by the heat and light, to draw 

 the figure of the interior, if extremely magnified. 

 Cambium or I shall now conclude the present letter with the explana- 

 tion of a term that h^s long demanded attention, particu- 

 larly on the subject oi seeds, which it concerns greatly. I 

 mean the word albumen or cambium, a matter found 

 wherever new wood is to be created. Duhamel calls it 

 cambium; Mirbel " la substance organisatrice," and gives 

 this description of it: " Soit que les fluidesy developpent 

 »* par ieur impulsion les cellules, et les tubes; soit qu'une 

 *■* puissance inconnue, y agisse seule et y determine ces 

 *' developpements ; soit, comme il est probable, que ces 

 •' deux causes combinees, y agissent de concert pour chan- 

 *' ger en tissu niembraneux la substance organisatrice, 

 *' &'c." I cannot think this is described with his usual 

 perspicuity, for he does not even show what it really is. 

 Mr. Ktiight makes it much more plain, but thinks it pro- 

 ceeds from the bark. Much as I have profited by his re- 

 marks, which always carry with thera the conviction, that 

 he has deeply studied the subject, I cannot agree with him 

 in this opinion. I have perpetually seen it grow on the dry 

 piece of a seed vessel, which I have placed icithin the graft 

 for the purpose ; in the same manner I have put the edge 

 of a knife, and a diminutive piece of muslin, and fpund 

 the cambium growing on thern, as on the wood, and bprk. 

 Now whence does this substance proceed? frorn the juices 

 of the plant alone, from the mixture of the sap with the 

 blood of the plant, resting on the part, and there forming 

 as a crystal, since like a crystal it is the produce of the 

 ioint juices. But it is very different from the jelly founcj 

 in the pocket, which also has been improperly called albu» 

 pien. 1 shall now give an account of it, describing its ap- 

 pearance 



