GEOWTH OF PLANTS. 127 



a large number of buds composed of leaves arranged round a 

 common axis ; each bud has the power of preserving its own 

 life and reproducing the original structure when removed 

 from the parent stem, if placed in circumstances favourable 

 to its growth, and yet all are connected in the growing 

 tree by a system of vessels which form a communication 

 between them. This is precisely the nature of those 

 structures which are formed by the animals of the class 

 that may be regarded as the most characteristic of the 

 group. Every mass of coral is the skeleton of a compound 

 animal, consisting of a number of polypes, connected 

 together by a soft flesh in which vessels are channelled 

 out ; the polypes are capable of existing separately, since 

 each one, when removed from the rest, can in time produce 

 a massive compound fabric like that of its parent, but they 

 all contribute to the maintenance of the composite structure 

 so long as they are in connection with it. In some instances 

 the skeleton is stony, and is formed by the deposition of 

 calcareous matter either in the centre of each fleshy column, 

 so as to form a solid stem, or on its exterior so as to form 

 a tube. In other cases it is horny, and then it may be a 

 flexible axis in a delicate tube. Both the stony and horny 

 corals often possess the form of plants or trees, and as their 

 skeletons are often found with no obvious traces of the 

 animals to which they belong, they have been accounted 

 vegetable growths." 



DESCRIPTION OE A YE&ETABLE AND ITS PAETS. 



As has been said before, it is extremely difficult to make 

 any distinction between the lower tribes of the vegetable 

 and animal kingdoms, and physiologists are not yet agreed, 

 with respect to some members, as to which kingdom they 

 belong. Their whole substance is made up of cellular 

 tissue, and there are but few distinctions of parts, forming 

 generally a broad foliaceous expansion called the " thallus," 

 as in lichens and sea-weeds, or a sort of root composed 

 of fibres and called the "mycelium," as in the fungi. 

 But, a very few steps higher, the distinctive characters 

 become so evident that they are impossible to be mistaken, 



