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VEGETABLE PHYSIOLOGY. 
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By ARTHUR HENFREY, Esq., F.L.S., Lecturer on Botany at St. George's Hospital. 
I771HE task of the physiologist is the investigation and determination of the laws of life ; that is to 
iv say, his object is to lay down rules or general principles describing the invariable succession of 
facts in the history of what we call living bodies. Thus, when we say it is a law of vegetable life that 
" the lower or simpler the organisation of a plant is, the more independent are its alimentary parts of 
one another," we express merely our belief in the invariability of the occurrence of certain series of 
facts, which always have succeeded one another in a certain order, so far as our experience enables us 
to judge ; namely, that when we divide a simple plant Like a Conferva, composed of single rows of cells, 
into lengths containing one or two cells, without injuring them, or when we see such plants becoming 
spontaneously divided into such pieces, we find that each piece can continue to live and grow, — while, if 
we take a vegetable of complicated organisation, such as any flowering plant, we can only divide it 
into as many pieces or slips as there are buds upon it, with any chance of obtaining a distinctly inde- 
pendent plant from such piece; these buds being, of course, complicated structures, containing 
thousands of cells of varied form and consistence. 
Now, there are few subjects on which greater variation of opinion exists, than on the nature and 
peculiar characters of this life, a want of agreement which may without hesitation be attributed to our 
ignorance. There exists in every department of science, except astronomy, — where we have attained to 
the conception of a single primary force, namely, gravity, — a large volume of facts which refuse to be 
arranged under the laws of the forces or secondary causes with which we are acquainted. This is 
particularly the case in the study of organized nature ; we are all acquainted with a vast number of 
facts which we cannot connect by any definite chain of causes with well-defined forces, and we say, for 
the moment, that they depend upon the exertion of vital force : using this term so vaguely, that it is to 
all intents and purposes a confession that we do not know the cause. The vital force is made to account 
for the residue or balance of facts which remain unexplained, that is unconnected with our knowledge 
of the other parts of nature. The great progress of chemistry during the last few years, and the 
extensive application of its conclusions that we have been able to make in vegetable physiology, have 
gone far in analysing and breaking tip into separate, well-defined notions, the general idea of the vital 
force of vegetables, taking a large number of facts out of the domain of vitality, and bringing them 
under the laws of chemistry and physics. A result of this has been, especially among chemists 
totally devoid of detailed knowledge of the phenomena of vegetable life, the acquisition of an idea that 
no such thing as a special vital force exists, and that all the so-called phenomena of life may ultimately 
be referred to physical causes. This is a simple consequence of looking only at one side of the 
question, and an illustration of the ill effects which may arise from the too great tendency to devote the 
mind to a single pursuit. The division of labour in science is a very different thing from the division 
of labour in the arts ; in the latter, men have to do with material objects which pass unchanged from 
hand to hand, but in science we have to do with ideas, which cannot be conveyed accurately and fully by 
words alone, except in regard to objects having the fewest possible qualities, qualities which the daily 
experience of life has made familiar. Even here, in daily life, no man could convey to another an 
idea of a blue or red colour if that other had not previously seen those colours and learned their 
peculiar names ; how much less, therefore, can accurate ideas of such complicated objects, baring such 
refined distinctions as occur in organic structures, be conveyed by words to those who have had little 
or no experience to give them a knowledge of the peculiar qualities, — to speak familiarly, " to give them 
pegs on which to hang their ideas ? " Hence the one-sided view of Mulder and his school, who have 
done so much to enlighten us on the chemistry of vegetation. To use the words of Prof. Sehleiden, 
they have forgotten that " cellulose is not a cell." The organic form — different, but in each case absolutely 
fixed in hundreds or thousands of instances, in which chemical analysis can point oat no distinction — at 
once marks the presence of some force over and above the physical forces. 
When, however, we come to the study of the phenomena of vegetable life, we find them so compli- 
cated, we find various changes so dependent upon physical and chemical agencies, that it becomes our 
first object to investigate and determine the influence of these as conducing to the effects. The residual 
facts to be attributed to vitality arc so few and so little within the sphere of our comprehension, mani- 
festing themselves only in the phenomena of form and continual change, that the greater part of our 
labour in the inquiry into the laws of vegetable life, resolve themselves into chemical and physical 
y investigations, the peculiar characteristic phenomena of vitality in vegetables lying chiefly in the 
j<a domain of morphology. Animal life presents a more complex condition ; there we have a high compli- 
c ™ cation of living forms, and physiology has to deal with a great variety of organs, and what are called 
