68 
ON THE NERVOUS SYSTEM OF VEGETABLES. 
analogous to, that which contracts the tissue of the lower 
animals. What is this power ? 
In organic structures we may recognise four fundamental 
systems of tissue, viz.:— 
The soft cellular tissue, 
The hard bony tissue, 
The contractile muscular tissue, and 
The energy-conveying nerve tissue. 
In the highest animals we find all those systems well 
developed. As we descend the scale we find them fading out 
in the order in which I have placed them. First the nerve 
tissue diminishes, then the muscular, then the bony, till the 
lowest organic forms consist of soft cells only. 
But since, according to the laws of organic Evolution, 
the highest forms have been developed from the lowest, the 
capacity for this development must exist in those lowest 
forms, in the same manner as the capacity to develop into 
an oak exists in the acorn. In fact, the first embryonic form, 
even of mail himself, is still a single cell. 
Now in the Vegetable Kingdom we find that the first two 
systems of tissue are well developed, the cellular and the 
bony. The third system—that of the laminated and con¬ 
tractile muscle, is imperfectly represented by the foliage 
which clothes the hard skeleton and with which most of the 
contractile movements are connected; but the last and highest 
system, that of nerve tissue, is quite undeveloped. 
The laws of true analogy, however, suggest the immense 
probability that this is only one of the regular phenomena of 
organic development; that the form of vital energy which 
constitutes thought and sentiment in man and which repre¬ 
sents itself in the material world by nerve tissue, exists through¬ 
out the descending scale of life in a gradually less developed 
condition till in the Protozoa and Badiata among animals, 
and in all vegetables, it is so completely embryonic that it is 
not represented to our senses by any differentiated tissue. 
From this point of view irritability in plants is seen to 
have precisely the same origin as in animals. 
It is a nervous phenomenon ; the result of nerve energy 
in its lowest form acting through contractile cells. In the 
most general sense the plant “feels” in the same way that 
the animal does, but probably in the most general sense only. 
No man can absolutely say what amount of consciousness of 
feeling may exist in any creature other than himself. But 
all the evidence we can gather points to the conclusion that 
consciousness is one of the highest conditions to which nerve 
energy attains, that it becomes continually less definite along 
the descending scale of life, and that in cellular animals and 
all plants there exists only a faint trace of it, or none. 
