138 THE STEM. 



It is the aggregate, the blended mass alone, that long survives. 

 Plants of single cells are alone perfectly simple, and their exist- 

 ence is extremely short. But the more complex vegetable of a 

 higher grade is not to be compared with the animal of the highest 

 organization, where the offspring always separates from the parent, 

 and the individual is consequently simple and indivisible ; while it 

 is truly similar to the branching of arborescent coral, or other 

 compound animals of the lowest grade, where successive genera- 

 tions, though capable of living independently and sometimes sepa- 

 rating spontaneously, yet are usually developed in connection, 

 blended in a general body, and nourished more or less in common. 

 Thus the coral structure is built up by the combined labors of a 

 vast number of individuals, by the successive labors of a great 

 number of generations. The surface or the recent shoots alone 

 are alive ; and here life is superficial, all underneath consisting of 

 the dead remains of former generations. The arborescent species 

 are not only lifeless along the central axis, but are dead through- 

 out towards the bottom : as, in a genealogical tree, only the later 

 ramifications are among the living. It is the same with the tree, 

 except that, as the plant imbibes its nourishment principally from 

 the soil through its roots, it makes a downward growth also, and, 

 by constant renewal of fresh tissues (216, 228) maintains the com- 

 munication between the two growing extremities, the buds and the 

 rootlets. We have seen that branches grow from the parent stem 

 just as this grew from the embryo, only that they are implanted on 

 the main trunk instead of the ground ; still they are capable of 

 living as independent individuals, and often do in various ways (as 

 by bulbs, tubers, layers, stolons, offsets, &c.) spontaneously ac- 

 quire a separate existence. The branches, therefore, or the buds, 

 which are the branches in an earlier stage, are real individuals, 

 which conspire to make up the composite tree. The contrary 

 view would lead to the absurdity of an individual consisting of sev- 

 eral genera and species ; since the Apple, Pear, Mountain Ash, 

 Quince, Medlar, and Hawthorn may all, by ingrafting, be com- 

 bined in a single tree. It would also oblige us to consider as a 

 single individual all the plants which have arisen from the mechan- 

 ical subdivision of an original stem, for example, perhaps all the 

 Lombardy Poplars in this country, or even a large part of the Po- 

 tatoes of Europe and America. While actually united, however, 

 all the branches are to some extent subordinate to the general 



