THE ORIGIN OF YEARLY PERIODICITY 213 



bears at the same time spring, summer, autumn, and winter shoots T . Each 

 bud shows the usual periodicity, but that of the plant as a whole has gone, 

 and it disappears at Tjibodas in the course of a few years. 



The same probably applies to the root also, which must in fact be 

 continually active, and which even in our climate has only a short resting 

 period. Direct experiment is, however, required to make this certain, and 

 also whether the periodicity as regards growth in thickness is lost. This 

 is probably the case in the main stem at least, for the secondary growth 

 of the stem in spring and autumn stands in close relation to the activity 

 and development of the branches and leaves. 



In the same way the vine at Cucumana in Venezuela 2 , and at Khartoum ;{ 

 in Central Africa, bears flowers and fruit all the year round, while the cherry 

 grows as an evergreen in Ceylon 4 . It has not, however, been determined in 

 any one of these cases whether the resting period of each bud remains the 

 same, is shortened, or disappears. Even the formation of bud-scales may 

 possibly be suppressed, direct development into a leafy branch occurring, 

 and this can in fact be induced by removing the spring foliage. 



While the observations made in Java show that the resting period may 

 entirely disappear under sufficiently constant conditions, those made at 

 Madeira show that an annual fall of temperature is sufficient to maintain 

 a yearly periodicity, although in the coldest month growth still remains 

 possible. Reiche observed the same in the sub-tropical climate of Chili, 

 and also found that a periodicity is more readily produced or maintained in 

 some plants than in others 5 - Thus in both Brazil and Madeira the peach is 

 almost an evergreen 6 , whereas the oak, beech, and apple still pass through 

 a long resting period. A similar yearly rhythm might be induced by 

 periodic drought, or by other periodic changes, under constant conditions 

 as regards temperature 7 . 



Grisebach considers that the yearly periodicity in plants of temperate 

 regions is entirely an hereditary property, whereas Askenasy considers it to 



1 Schimper, Pflanzengeographie, 1898, p. 266. 



* Quoted after von Humboldt by de Candolle, Geographic botanique, 1855, T. I, p. 392. 



3 According to Harnier. Cf. Linsser, Ueber d. period. Lebenserscheinungen, 1867, 2. Abth., 

 p. 81 ; Askenasy, Bot. Ztg., 1877, p. 841. 



* De Candolle, 1. c., p. 391. Junghuhn observed thnt the peach and strawberry bore blossoms 

 and fruit all the year round. On the behaviour of the strawberry and some other plants in Brazil 

 cf. Miiller, Bot. Jahrb. f. Systemat. u. Pflanzengeographie, 1882, Bd. II, p. 394. The absence of 

 fruit from the cherry in Ceylon, and from most of the European fruit-trees grown in British Guiana 

 (R. Schomburgh, Reisen in British Guiana, 1847, Bd. I, p. 45), is probably the result of the high 

 temperature. A plant may become evergreen owing to the lengthened duration of the leaves 

 without the time of flowering altering. Cf. Kraus, Bot. Centralbl., 1882, Bd. IX, p. 75. 



5 Reiche, Jahrb. f. wiss. Bot., 1896, Bd. xxx, p. 98. 



6 Harting (cf. Askenasy, Bot. Ztg., 1877, p. 834) states that peach-trees may in part blossom 

 in November at Madeira. 



7 Cf. Schimper, 1. c., p. 267. 



