. PHYSIOLOGY. 283 
@ats, (Avena sativa), was killed in this manner by 
Serratula arvensis. 
Flax, (Linum wsitatissimum), by the Scabiosa arvensis 
and Euphorbia peplus. 
Wheat, (Triticum aestivum), by Erigeron acre. 
Buck-wheat, (Polygonum Suda id Spergula 
ATVENSIS» 
Carrots, (Daucus carota), by the Inula Helenium, and 
that the different weeds, as they are called, hinder 
thus the growth of the above plants. From this ob- 
servation, if it should be confirmed by further re- 
searches, the antipathy of different plants might be 
explained.’ But might not the growing of the one 
and the death of the other be explained upon the 
simple principle, that, as weeds consume the same 
food with cultivated plants, the first perhaps take 
up ‘the nourishing matter with a greater velocity ‘ 
This remains still to be determined. 
S276. 
The nature of the circulation of sap in plants,-is 
at present still) involved in great obscurity. In our 
times nobody, I suppose, will choose to maintain with 
with Jampert, mathematically, that plants have no 
vessels, as Grew, Malpighi, Muftel, Moldenhawer and 
Hedwig have stated and proved their presence long 
ago, and eyen ocular inspection may convince all re- 
maining sceptics of this truth. Notwithstanding, how- 
ever, we are still 1gnorant of the manney in which the 
sap passes through these channels. Dr Hales ascribes 
the ascent of the sap to the rarification of air and ca- 
pillary attraction. Some allege, that the sap ascends 
during 
