INTRODUCTION. 



That the substance of the more perfect plants consists of 

 layers of different constitution was a fact that could not escape 

 the most untutored observation in primitive times ; ancient 

 languages had still words to designate the most obvious ana- 

 tomical components of plants, rind, wood and pith. It was 

 also easy to perceive that the pith consists of an apparently 

 homogeneous succulent mass, the wood of a fibrous substance, 

 while the rind of woody plants is composed partly of mem- 

 branous layers, partly of fibrous and pith-like tissue. The 

 obtaining of threads for spinning from the rind of the flax- 

 plant, for instance, must have suggested some idea, if only 

 a vague one, in the earliest ages, of the way in which the 

 fibrous could be separated from the pulpy part of the bark 

 by decay and mechanical treatment. Neither Aristotle nor 

 Theophrastus failed to compare these components of veget- 

 able substance with corresponding ones in animal bodies, and 

 it has been already shown in the first book how Cesalpino, 

 following his masters, took the pith for the truly living part of 

 the plant and the seat of the vegetable soul, and applied this 

 idea in his morphology and physiology. He remarked that the 

 root generally has no pith, and that the part of the root which 

 answers to the wood of the stem is often soft and fleshy ; the 

 composition of the leaves from a green and succulent substance 

 and strands of fibres at once suggested a certain resemblance to 

 the green rind of the stem ; and it was evidently this which led 

 him to consider that not only the leaves, but also the leaf- 

 forms of the flower-envelopes had their origin in the rind of the 



