290 METAMORPHOSIS 



the roots of maize grow at a relatively uniform rate, for with approximately 

 half-hourly observations he obtained the following increases in growth calcu- 

 lated up to one hour : — 



Growth increments, calculated by micrometer (i = ^\ mm.). 

 Hours I 23456789 



Root No. I 340 270 30.0 29-5 360 350 380 31-0 33.5 

 Root No. 2 325 34.5 37-9 34-5 33-0 33-6 330 — — 



These growth increments may be, therefore, considered as relatively uniform, 

 while in other bodies for the most part much greater variations have been ob- 

 served, variations the causes of which are not known, and which we may describe 

 as 'spasmodic growth variations'. If the observation of a root be carried on 

 not merely for several hours but for days or weeks, we find that the total growth 

 also shows a * grand period ' (Pedersen, 1874). 



The growing point of the shoot is, as we have seen, enclosed by leaves 

 growing more rapidly than the apex itself and thus forming a ' bud '. In many 

 annuals and perennials, and also in some trees, we find at the growing point, 

 during the whole summer, the rudiments of new leaves and the parts of the axis 

 relating to them ; they at once become transformed from the rudimentary con- 

 dition into the adult by elongation. This is not the case with the majority of 

 trees. In these cases during summer and autumn all the parts of the bud within 

 the leaves, which act as bud-scales, undergo slow embryonic growth, and these 

 parts become unfolded in the following year. In this case embryonic growth 

 and growth in length are sharply separated. Thus in many Coniferae one sees 

 in autumn, after removal of the bud-scales, a green cone several millimetres 

 long covered with small spirally arranged outgrowths. This is the rudiment 

 of an entire shoot which will elongate in the following year in the course of a few 

 weeks. In other trees the same features are seen, but the buds for the most 

 part are not so easily examined as in the case of the spruce. The elongation, 

 however, may take place in a few days (beech). 



The cases in which growth consists merely in the elongation of parts laid 

 down in the previous year are the simplest to understand, and we will begin 

 with them. Two types have to be distinguished (Rothert, 1894). The whole 

 bud may behave uniformly and grow approximately equally in all its parts, or 

 exhibit a distinction into nodes which grow but little and internodes which grow 

 vigorously. The unsegmented bud axis of the spruce, which may serve as a type 

 of the unsegmented shoot, becomes uniformly elongated in springtime through- 

 out its entire length, and may become five times as long as it was during the 

 winter, attaining in this way about one-tenth of its ultimate length. In the 

 course of further extension a zone of maximum growth appears, which lies at 

 first at the base of the shoot, but passes gradually nearer and nearer to the 

 apex. Exact measurements demonstrate the fact that each individual zone 

 of a spruce-shoot passes, during its elongation, through a grand period. 



Let us now compare the bud of Fritillaria with that of the spruce. This bud 

 is divided into nodes and internodes, but one only of the many internodes 

 elongates actively, and a grand period may be demonstrated in its case with 

 the greatest readiness. The following table gives relative elongations of this 

 internode (Sachs, 1872, 129) : — 



Day 123456 7 8 9 10 II 12 13 14 15 16 17 18 19 



mm. 2.0 5.2 6.1 6.8 9-3 ij-^ 12-2 85 io-6 10.3 6.3 4.7 58 4-4 3-8 2-0 1-2 0-7 o 



If, finally, all the internodes of a bud become elongated (as, for example, 

 in the case of the horse-chestnut) we obtain just as many growth zones as there 

 are internodes, separated by nodes which grow slightly or not at all. Each 



