346 METAMORPHOSIS 



present in quantities almost as great as in autumn ; this starch is then dis- 

 solved and employed in the construction of new shoots. The close of the 

 special resting period coincides in a remarkable manner with the date when the 

 amylaceous contents are at a minimum ; only when all the starch is dissolved 

 do we succeed in inducing the development of shoots, and apparently every 

 increase in temperature at this moment induces a progressive re-formation of 

 starch. Conversely, the dissolution of starch in autumn can be induced by 

 lowering the temperature. Of course these transformations of reserves must 

 not be looked on as the causes of periodic rest, they are to be referred to a 

 common cause, possibly to an alteration in the protoplasm itself, which governs 

 all metabolic processes. 



Detailed research on our native trees would certainly conduce to the 

 extension of our knowledge of this interesting problem in many ways, since none 

 of the various cultivated varieties of the same species behave identically as 

 regards their resting periods QOHANNSEN) ; so much the greater then must be 

 the differences between different species of trees. It is also well known that 

 different organs of the same plant exhibit striking variations in their resting 

 periods. Secondary growth in thickness, which commences usually about the 

 same time as the unfolding of the buds, lasts considerably longer than leaf forma- 

 tion, at least in those trees whose buds open spasmodically, and xylem ceases 

 forming in summer earlier than phloem (STRASBURGER, 1891). The entire 

 process, however, always exhibits a definite periodicity such as that described, 

 viz. activity in summer and rest in autumn and winter, the close of the period of 

 secondary thickening certainly not being directly dependent on external condi- 

 tions. The roots of trees differ greatly in this respect from shoots. Owing to 

 the obvious difficulty of research the problems connected with root growth have 

 been as yet little elucidated, and investigators (RESA, 1877 ; WIELER, 1893 ; 

 BUSGEN, 1901 ; HAMMERLE, 1901) have not been successful in making a perfect 

 comparison of the two types of organ. This much is certain, however, that 

 in many roots growth begins in March and continues till November or Decem- 

 ber; in the middle of summer a marked decrease in growth may be frequently 

 observed, which never amounts, however, to a complete stoppage. No experi- 

 mental researches are as yet forthcoming, especially on the influence of external 

 conditions, such as heat and moisture, but such researches are absolutely essen- 

 tial before we can arrive at any decision on the periodicity of growth in the root. 



Many perennials may be compared 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 commencement 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 during the 

 winter cold, and may be temporarily at a standstill. This hibernation is, however, 

 an induced one, and on the temperature rising 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 off so that in midsummer the plant is reduced to its sub- 

 terranean parts only. Colchicum holds a special position among spring flowers 

 because the flowers appear, as is well known, from August to October, at the same 

 time as the new roots, while the leaves appear for the first time in the following 

 spring. Precedence of foliage by flowers is a phenomenon of widespread occur- 

 rence among spring plants, the peculiarity in the case of Colchicum, however, lies 

 essentially in this, that external factors prevent a rapid sequence of the foliage 

 shoots. In arctic countries and on high mountains the simultaneous forma- 

 tion of leaves and flowers is, however, a normal occurrence (WIESNER, 1902). 



