Q9Q MOTION OF THE SAP. 



Experiments and increafed vigour given ; and, the fame caufes operating 



and obfervations 'through fucceffive feafons, will give the afcendancy we gene- 

 ©n the motion of ° . . .. . °. , , 



the fapin trees. ril ''y obierve in the perpendicular branch. 



In the preceding experiments, none of the layers, or cuttings, 

 exceeded a few inches in length ; and, to the fummit of thefe 

 the lap appeared to rife, through the inverted tubes of the wood, 

 nearly as well as in thofe which retained their natural pofition. 

 Butfome former experiments had induced me to fufpedt, that 

 this would not be the cafe in longer cuttings ; I therefore planted 

 in the autumn of 1802, twelve cuttings of the fwallow, (Salix 

 caprea,) inverting one half of them. The whole readily emitted 

 roots, and grew with luxuriance; but their modes of growth 

 were extremely different. In the cuttings which Hood in their 

 natural pofition, vegetation proceeded with mo ft vigour at the 

 points moft elevated ; but in the inverted cuttings, it grew more 

 and more languid as it became diftant from the ground, and 

 nearly ceafed, towards the conclufion of the fummer, at the 

 height of four feet. The new wood alfo, which was generated 

 by thefe inverted cuttings, accumulated above the bafes of the 

 annual moots, as in the preceding inftances. 



Thefe fads appear to prove, that the veflels of plants are not 

 equally well calculated to carry their contents in oppofite di- 

 rections ; and, I think, afford fome grounds to fufpect that the 

 veffels of the bark, like thofe which conftitute the venous 

 fyftem of animals, (to which they are in many refpecfs analo^ 

 gous.) may be provided with valves, whofe extreme minutenefs 

 has concealed them from obfervation. 



The experiments, and ftill more the plates, of Hales, have 

 induced naturalifts to draw conclufions in direct oppofition to 

 the preceding. But the Plates of that great naturalift are not 

 always taken correctly from nature; * and Plates, under fuch 

 circumftances, however fair and candid the intentions of an 

 author may be, will too often be found ibmewhat better calcu- 

 lated to fupport his own hypothefis, than to elucidate the facls 

 he intends to ftate. 



The preceding peculiarities in the growth of in verted cuttings, 

 appear to have efcaped the obfervation of Du Hamel ; and, as 

 very few inftances of error, or want of accurate obfervation, 



* The eleventh Plate (Vegetable Staticks) is that to which, in 

 this place, I particularly allude. 



will 



