352 PHYTOLOGT. 



A bean grows by shoots ; every shoot is almost the only addition to 

 the plant ; however, not entirely so, for it grows a little in all its 

 former shoots, but that growth is proportional to the age of the shoot. 

 For example, if there are three shoots, and a fourth beginning to grow, 

 or growing, the third shoot grows a little while the fourth is increasing, 

 and more thau the second, and the second grows more than the first. 

 The first shoots seem to lose their power of growth in proportion to the 

 number of shoots beyond them ; so that by the time there are five, six, 

 or seven shoots, the first has hardly any perceptible growth : or every 

 new shoot may be supposed to stop the growth of the first one degree ; 

 or a new shoot does not begin to grow till the last has grown almost its 

 full length. Cut off the top shoot before it has grown its full length, 

 and it will continue to lengthen, but not so much as if the top had been 

 left on. 



The last shoot of a plant is always the weakest part of that plant, 

 and the last part of that shoot is the weakest part of that, and of 

 course the weakest of the whole. This fact is best known in severe 

 winters, or a cold beyond the natural temperature of the plant ; for 

 when the cold has been too great, we find that the last shoot either 

 dies, or if not so severe as to kill the whole of the last shoot, it shall 

 kill the last-formed part, so that new shoots are obliged to rise from 

 those branches that are two years old or more. 



Trees, after a certain period of their growth, which is pretty early, 

 but more so in some than in others, generally make shorter and shorter 

 shoots every succeeding year of their growth. But as the number of 

 branches increases, it is more than probable that not only the number 

 of branches of any one year's growth, but also the quantity of vege- 

 table matter added, exceeds that of any former year. So that, although 

 this year's shoots (taken separately) are shorter than those of last year, 

 yet the tree has gained, not merely in an additional progression, viz. by 

 adding the same quantity yearly ; but perhaps in a geometrical pro- 

 gression, which is a much greater rate of increase. 



Most plants have their periods of growth and periods of rest, inde- 

 pendently of variations of seasons, such as heat and cold : for in the 

 same degree of heat a tree may rest from growth, and then begin to 

 grow again. Perhaps this cessation from growth arises from the forma- 

 tion of seed going on in the plant, or endeavouring to go on, or because 

 it is the time it should go on in that plant ; and when that period is 

 over — the season remaining favourable respecting heat — the plant begins 

 to grow again, producing what is called the second growth. This 

 second growth of the branches of plants appears to be a continuation of 



