.N P R V NriPLfi^S^ t) F VEGETATION. 347 



bpen in diffefen't dire(5l;ionfs." In the walnut, after a certain age, it ap- 

 J)ears in the form of k regular tran'iverre hollow divifion. In fome plants 

 it-is altogethej; wanting; while in others^ as the fonchus, nettle, &c. there 

 is only a tranlVerfe partition of it at every joint. Many other varieties 

 might be mentioned. " " i^. . , : . 



The leaves of plants cpnmt of the fame fubftance with the trunk. 

 They are full of nerves "or woody portions, running in all directions, and 

 bf'anching out into innumerable fmall threads (Interwoven with the pa- 

 renchyma) Jik? Rnc lace or gauze. 



'The fkin of the leaf, like that of an animal, is full of pores, which 

 !^6t1i ferye for perfpiration, and for the ablbrption of dews, air, &c. 

 Thefe pores, or orifices, differ both in fhape and magnitude in different 

 plants, which is the caufe of that variety of texture or grain peculiar to 

 every plant. ,'"'.,. 



The pulpy or parehcTiymatpus part confifts of very minute fibres, wound 

 up into fmall cells or bladders. Thefe cells are of various fizes in the 

 fame leaf. 



All leaves,, of whatever figure, have a marginal fibre, by which all 

 tlie reft are bounded. The particular fhape of this fibre determines the 

 ftgure of the leaf. 



The veflels of leaves have the appearance of inofculating; but, when 

 ■Examined by fhe microfcope, they arc found only to be interwoven, or 

 laid along each other. 



What is calleci air-veflcls, or thofe which carry no fap, are vifible 

 even" to the naked eye in fome leaves. When a leaf ii (lowly broke, 

 they appear like fmall woolly fibres, conne6ted to both ends of the broken 

 piece. •'''-- 



The texture, vefTcls, i&c. of flowers arc pretty fimilar to thofe of the 

 leaf. ,, V 



Every .flower is perfediy formed many months before it appears out- 

 wafdly; that is, the flowers which appear this year are not, properly Ipeak- 

 in^, flowers of this year, but of the laft. For example, mczereon gene- 

 rally flowers in January ; but thefe flowers were completely formed in 

 the month of Auguft preceding. By lepatating the coats of a tulip- 

 root about the beginning of September, we find chat the two innermofl: 

 form a kind of cell, in the centre of which fl:ands the young flower, 

 which is not to make its appearance till the following April or May. 

 ' In deferibing' the ftrudure of fruits, a few examples Ihali be taken 

 from fucH as are moft generally known. 



Part VI, No. jz. 3 N A Pear, 



