76 



COUESE OF THE SAP. 



PT. II. 



is true of them, and also of the silver ends of woody- 

 roots ; but it must be recollected that to neither of 

 these can the air be admitted when they grow in water, 

 or light when they grow in earth. It is however, I 

 believe, true of these unripe ends of roots, under any 

 circumstances. But when part of a woody root is 

 accidentally exposed by the wearing away of a bank, 

 &c., the layer below the outer circle will be found 

 green, precisely the same as on a branch ; though 

 where the root goes under the ground, both nearer 

 and farther from the stem, the under layer will be 

 white. The layer under the outer cuticle may also be 

 observed green at the commencement of the root of a 

 young tree, when it is accidentally exposed near the 

 neck of the plant. This is not a matter of opinion, but 

 a mattter of fact, and we have only to use our eyes to 

 see it. 



On the other hand, since writing this, I have ob- 

 served that, in those parts of the stems of seedlings 

 which pass through earth, the piths and the herbaceous 

 That roots envclopcs are as white as those of roots. I say those 



have no 



piths an Qf roots, for I have also observed that the tap-roots of 



error. ' J- 



seedlings have piths of precisely the same size as the 

 stems. And I doubt not it will be found that the roots, 

 as well as the stems, consist solely of alternate layers of 

 pith and wood, with one outer skin or cuticle. If 

 roots have no piths, what are the rays or silver grain 

 in the roots of oaks ? Non-medullary rays ? In the 

 experiments detailed farther on, with a view to induce 



