t. 



J 



rface^ 



old 



sof 



orth 

 bofi 



c 



• Water 

 ir-cells 



caufe, 

 hich is 



it in its 

 I to fif, 



ilj dif. 

 •pofe 6f 



natomjr 

 , which 



Jee Bo- 



[ hy the 

 at their 

 human 

 Is there 

 : of this 

 a net* 



^aquatic 

 oints,a5 



-ranun- 

 fome 



ffon^ 





aves 



are 



ive 



uatic 



thus 



# 



Sect.IV. III. !• 



AND VEINS. 



4; 



th 



eir 



furfaces wonderfully enlarged for the purpofe of acqu 



water 



nd 



combined oxygen from the air, which is diffufed in the 

 which abounds fo much lefs there than in the atmofphere ; for the 

 fame purpofe the plants on the fummits of high mountains^ where 

 the air is fo much rarer, and confequently abounds lefs with oxygen, 

 have their leaves much more divided than in the plains, as pimpinella, 

 pctrofelinum, and others, that they may expofe a more extenfive fur- 

 face of vefiels to the influence of the thinner atmofphere. 



3 



Th 



argement of the furface by fo minute a divifioa 



does not however feem to be the only ufe of this uniform ftru£lure 

 of gills and aquatic leaves ; but there is another very important one, 

 which hath hitherto I believe efcaped the notice of philofophers ; and 

 that is that points and edges contribute much to the feparation of the 

 air, which is mechanically mixed or chemically diflblved in water, as 

 appears on immerfing a dry hairy leaf into water frefh from a pump. 



which innuriierable elobules of 



t> 



ke quick-fil 



appear 



almoft every point. Nor is it improbable that points immerfed in wa- 

 ter may in a bright day contribute to decompofe it, or certainly to fet 



liberty its fuperabundant oxygene 



the perfpiration of 



leaves when expofed to the funfhine, and to the green matter in the 

 experiments of Dr. Prieftley, which is probably owing to the fine 

 points of both of them ; and laftly, when points of filk are immerfed 

 in fpring water, which is frequently hyperoxygenated, as in the ex- 

 periments of Count Rumford, related in the Philof. Tranfad. See 



Sea. XIII. 1.5. 



III. I. The roof-leaves of many perennial plants, which do not 

 produce flowers in the firfl: year from the feed, are different from thofe 

 of future vears, as in the rheum palmatum, palmatcd rhubarb, the 



years, as in 



; fmall and nearly circular, and not divided into fingers till 



the fecond year ; and in tulip the leaf the firfl: year from the feed is 

 fmall like a blade of grafs, rifing from a diminutive bulb. In othet 



perennial plants the root-leaf is undivided, but at the fame time larger 



than 



