MURRAY ON THE COURSE OF THE SAP. 
3 
channel. Any stream, after being released from a narrow gully, 
behaves in this way, and the wide-spread waste of stones and 
gravel radiating like a fan from the mouth of a gorge is one of the 
most striking features of any landsoape where this occurs. 
2. As to the Physiological Experiments, these are chiefly the 
phenomena relied on by Sachs as warranting his conclusion that light 
is essential to assimilation, and that this can only take place in 
the leaves, and consequently that all assimilated products that are 
found elsewhere must necessarily have descended from the leaves 
in the form of elaborated sap. As to these, I would only say here 
that neither his facts nor his reasoning seem to me to bear out his 
conclusions. 
3. As to the Chemical Experiments, it appears to me that it 
will he found on examination that there are in them more pheno¬ 
mena than one mixed up together, and that what was referable 
to the one has been applied to the other. 
But it is not my object to attack these views on the present 
occasion. 3dy immediate purpose is to ascertain, what according to 
the best lights of science we are expected to believe on the subject. 
I have thought that it might be desirable to elicit an expression of 
opinion on the subject from a body like this committee, whose 
competence to speak with authority on such matters is universally 
recognised. I knowhow difficult it is to supplant old opinions—what, 
an exertion of magnanimity is required to acknowledge that we have 
been in the wrong. I remember, with sympathetic distress, the almost 
piteous remonstrance of a learned Professor at the Congress at Brussels, 
who, when interrupted in his argument about the descent of the, 
sap by cries of “ 11 n’y a pas deseve descendants” exclaimed, “ There 
must be a descent of the sap. I have been teaching it for thirty 
years. What am I now to say to my students if there is no descent 
of the sap ? ” But the greater the difficulty the more the necessity 
for conquering such feelings, and putting the question on its right 
basis. 
I am not at all blind to the consequences of adopting the view 
that I take. I know that if descent of the sap goes, the elaboration 
of any sap by the leaves beyond Avhat is necessary for their own 
needs must follow. If it is not to descend, of what use is it to, 
elaborate it in them, and why elaborate it hy the leaves rather than 
by the roots or any other part ? The nutrition of plants by free 
carbon-dioxide takenfrom the atmosphere throughtheleaves will also, 
have to go. The nutrition of carnivorous plants will become still more 
difficult to comprehend, and other more remote corrections on received 
a 2 
