SUPPLEMENT 107 



of root-growth. Owing to the obvious difficulty of research the problems 

 connected with root-growth have been as yet little elucidated, and investi- 

 gators (RESA, 1877 ; WIELER, 1893 ; BUSGEN, 1901 ; HAMMERLE, 1901 ; 

 A. ENGLER, 1903) are not in accord on the subject. This much is certain, 

 however, that in many roots growth begins in March and continues till Novem- 

 ber or December ; in the middle of summer a marked decrease in growth may 

 be frequently observed, which scarcely amounts, however, to a complete 

 stoppage. No experimental researches are as yet forthcoming, especially on 

 the influence of external conditions, such as heat and moisture, but such 

 researches are absolutely essential before we can arrive at any decision on 

 the periodicity of growth in the root. In all probability this periodicity is 

 much more dependent on external factors than that of buds. 



Perennials also often exhibit a marked periodicity, and many agree with 

 trees as regards the mode of development of the leafy shoot. A peculiarity, 

 however, appears in our spring flowers, where apparently the resting period is 

 transferred to the dry season of the year, the actual summer. The commence- 

 ment of the new growing period generally occurs in these plants in autumn, 

 and shows itself first in the formation of new roots. The buds also begin to 

 develop in October and November, but do not as yet come above ground. 

 Further development is retarded by the winter cold, and may be temporarily 

 brought to a standstill. This hibernation is, however, an induced one, and if 

 the temperature be raised, all these plants are easily induced to shoot in winter. 

 In nature the formation of flowers and foliage takes place in the early spring, 

 according to the species, from February to May. Early in the summer the 

 leaves fall away, so that in midsummer the plant is reduced to its subterranean 

 parts only. 



More exact investigation shows us that the differences between spring 

 plants and trees are by no means deep-seated. The summer rest of the former 

 may be readily compared with the absence of leaf-unfolding in summer in all 

 intermittently-budding trees ; the foliage-leaves of such plants die off much 

 sooner than in the case of trees, but it can scarcely be doubted that embryonic 

 growth continues during the whole summer in the subterranean organs. Nor 

 is the early commencement of vigorous growth in the buds in autumn so very 

 extraordinary, since, according to ASKENASY, the buds of trees do not cease 

 developing during the winter. The characteristic feature of spring plants lies 

 only in this, that their periods are somewhat moved forward and that their 

 leaves are very short-lived. They also exhibit a resistance at certain times to 

 artificial forcing ; thus tulips and hyacinths cannot be made to flower before 

 December, and many kinds of potato cannot be made to shoot in autumn. 

 But in their case also it is possible to induce an early development, if the organ 

 in question be in the first instance prevented from hibernating, as SCHMID (1901) 

 has succeeded in doing in the case of the potato and KLEBS (1903) in the 

 hyacinth. 



What conclusion then may we draw from the fact that it is possible to 

 shorten considerably the resting period in trees and perennials in which a well- 

 marked resting period occurs ? KLEBS appears to think that it is possible to 

 induce a continuous leaf-formation quite generally by using the appropriate 

 means, but we cannot agree with him in this. It appears to us that in many 

 plants the periodicity is unchangeable because in their case there is no con- 

 tinuous and uniform formation and evolution of foliage-leaves. Although it is 

 possible, perhaps, to induce a tree like the beech, which shoots periodically, to 

 go on doing so continuously, it does not necessarily follow that there is any 

 prospect of making a bulbous plant do so. The formation of a certain number 

 of foliage-leaves must always lead to the evolution of scale-leaves at the terminal 



