OF GROWTH IN TREES. 95 



ward the bottom of each shoot, we have formed a series of 

 perfectly undeveloped internodes, which support the covering 

 leaves, and which are visible after their fall in a series of closely 

 approximated annual scars, called, in this work, bud traces 

 (gemma vestigia). Then follow the partially developed inter- 

 nodes of the lower leaves of the shoot, and then the principal 

 internodes which, through their expansion, form the shoot. 

 But the vitality of the leaves above the centre of the shoot 

 becomes more and more enfeebled, because they come to their 

 perfection later in the season, when the heat and light of the 

 sun those stimulants ef vegetable vitality decrease. The 

 internodes between the leaves consequently approach each 

 other, until finally we arrive at the terminal bud, where the 

 shoot again enters on the stage of rest. 



Now, as the same cycle of accelerated and retarded growth 

 is repeated each season, and since there is always as marked a 

 contrast among the shoots as between the internodial develop- 

 ments of the commencing parts and those that follow, the 

 same wave of growth is perceptible amongst the shoots ; and 

 therefore we have marked out by Nature, in a manner 

 not less sure, the growth of the year, in cases where the 

 bud traces are indistinct or wholly absent from the axis of 

 growth, as in the Buckthorn (Rhamnus frangula). In the 

 Beech branch, represented on page 31, the wave of growth 

 appears to culminate about the centre of each year's shoot. 

 The reader will be satisfied of this fact by examining the 

 drawing. 



The Daily Wave. According to Treviranus, the growth of 

 trees is accelerated during the day and retarded in the evening. 

 The principal German physiologists appear to agree as to the 

 fact that there is such a daily acceleration and retardation of 

 growth, though they differ a little as to the precise time of its 

 occurrence. This daily fluctuation is by no means unreasona- 

 ble ; for growth can only take place through the assimilation 

 of formative material, and this mainly depends on the sun's 

 influence. The vital energies of plants may possibly vary with 

 the degree of the sun's elevation above the horizon, and plants 

 may recuperate to some extent during the night, like the animal 



