156 OESANIC METAMORPHOSIS OF LEAVES 



carefully excluded. Under such circumstances, the nume- 

 rous fully-formed embryo-growths of the next year on the 

 branches, are as secure under the covering-leaves of the 

 bud, as was the solitary embryonic shoot and leaves of the 

 first year under the wrappers of the seed. 



To the tree, as well as to the annual, winter is the season 

 of rest ; and exhausted vitality, in both instances, has time 

 given for recuperation. In annuals, the exhausted vitality 

 of the roots, stem, leaves, flowers, and seed-vessel, or peri- 

 carp, retires into the seed; and, as the whole plant perishes, 

 these seeds become detached from it, and the embryos 

 which they inclose develope into new and separate plants 

 on the soil. But in trees the exhausted vitality, not only 

 of the leaves but of the new layer of bark and wood-cells, 

 which they have constructed (see page 64), retires into the 

 buds, from which the new plants develope on the return of 

 Spring. ISTow, although there are cases amongst herbaceous 

 plants, as for example, Lilium lulUferum, in which axillary 

 buds are formed by the leaves which become detached from 

 the stem and grow into separate and independent plants 

 on the soil, no such instance occurs in trees. The buds of 

 trees, formed by the leaves of each season, do not separate 

 fi'om the tree ; and hence the new plants which they con- 

 tain, remain organically united with each other about a 

 common axis. This is the reason why the vegetative period 

 in trees is so greatly prolonged, and why they attain such a 

 superior altitude and spread. They rest each winter, and 

 through perennial associations of new growths, iNature 

 carries on her work much further than in herbaceous 

 plants. Trees are, therefore, composite plants, developed 

 on the grandest scale. They cover a far greater extent of 

 ground than herbaceous plants. Hence their giant forms, 

 when gathered together into communities, are most strik- 

 ingly seen in the landscape pictures of the earth. A firmer, 

 more enduring foundation is thus laid, in the organism of 

 trees, for the exercise of the reproductive function ; and 

 when once the state of puberty is reached, they are neces- 

 sarily covered with the utmost profusion of flowers, and 



