530 



is imicli smaller. An investigation at Utrecht on Ihe size of tiie 

 adnlt tlorul buds, just before flowering, showed some diversity, 

 probably connected with the fact that not all buds opened on the 

 same day, and that the flowering extended over two days. This was 

 repeatedly the case at Utreciil, but also at Ikiitenzorg stragglers are 

 sometimes found, which only open on the day after the general 

 flowering, although it is not so common there as at Utrecht. Probably 

 this is due to a more rapid development under the favourable con- 

 ditions of the trojncs. Carefid observation indeed shows, that the 

 opening of the flowei's is not absolutely synchronous and that it 

 takes place at different hours ; nor is the end of the flowering 

 reached simultaneously, for it may vary by some hours or even by 

 half a day. Moreover the interval between opening and fading is not 

 identical for diiferent flowers. 



Attempts to induce flowering experimentally, by a choice of external 

 conditions, have not yet furnished any result. Such attempts are 

 rendered all the more difficult by the necessity of having plants 

 bearing buds at the desired stage of development. 



The phenomena shown by Dendrobium crunienatum do not indeed, 

 differ fundamentally from those observed in other Orchids. In these 

 also the simultaneous flowering of different plants is often seen, but 

 it is less striking, because the flowering generally extends over days, 

 or sometimes e\'en over weeks and hence one flower may open 

 several days before the other. 



Still more generally the flowering of the "pigeon orchids" may 

 even be regarded as the extreme case of what is observed with 

 respect to the flowering of plants in our own climate. Here also, 

 for instance in spring-flowering plants, the floral buds reach an 

 advanced stage of development, which is not passed, until external 

 conditions are favourable and then simultaneous flowering of numerous 

 individuals occurs; the simultaneity is only less striking because the 

 last stages of development are gone through more slowly. Of late 

 these phenomena have been repeatedly investigated, e.g. by Ki.ebs ; 

 a plant like Dendwbium crumenatum would perhaps be a suitable 

 experimental object for a further investigation of these cases. 



Utrecht, August 1915, 



