528 



in deteniiiniiig- the flowering period, it should be noted thai Ihe two 

 above mentioned plantlioiises in Utrecht supply an indication, for 

 here Ihe differences could al most extend to the amount of light, 

 the 'temperature and the degree of humidity of the air. Observations 

 at Huilenzorg (and also earliei' ones at Tegal) have shown that the 

 light may here be dismissed from considoralion, for the flowering 

 time is the same for plants growing in the shade as for those in 

 sunny places, although ihe mnnhi'i' of the flowers is evidently 

 determined to some extent by the amount of light. Temperature and 

 degree of humidity on the other hand, probably both influence the 

 flowering time, or sometimes the one and sometimes the other of 

 these factors. At Buitenzorg it was occasionally noticed that heavy 

 rains, following a period of drought, soon induced an abundant 

 flowering of Dendrobium crumenatum. On Ihe other hand the co- 

 incidence of the spring flowering in plant houses at Bonn, Hamburg 

 and Utrecht can only be attributed to the temperature. During winter 

 the temperature of such houses is kept very constant; when in 

 spring the sun becomes more powerful, their temperature rises con- 

 siderably. It was indeed remarkable, that the above mentioned 

 coincidence was preceded hy a period of bright, sunny weather 

 over the whole of Western Europe. 



In what way can we now imagine the external conditions to 

 bring about tlie simultaneous flowering of very different individuals 

 of the same species? The explanation may be as follows: The buds 

 of this Dendrobium develop up to a certain stage, but cannot pass 

 it, unless certain favourable conditions are found in the environment, 

 e.g. of temperature or of humidity, or of both ; then these conditions, 

 acting for a sufficient time, give an impulse, which carries the buds 

 to their last stage of development; it is further necessai-y that these 

 last stages should be gone through in a very short time. 



What is observed in a state of nature is in complete agreement 

 with this explanation Not only are many flowers found at one time, 

 and few, or even a single one at another time, but different plants 

 do not behave in the same manner. We do not mean by this so 

 much that some plants always flower abundantly and others sparingly 

 (for this is more likely Ihe result of internal disposition, of which 

 we know as yet very little) but rather, that on one and the same 

 plant sometimes many flowers unfold, sometimes only a few. The 

 favourable circumstances were present, but there were not always 

 the same number of buds in the sensitive stage, sometimes not even 

 a single one, so that there are flowering days when a given plant 

 unfolds no flower, other days, when the number of open flowers is 



