32 THE FLOEA OF SINGAPORE. 



is not rare however to find certain plants of Pigeon orchid which 

 do not flower on the regular day, but have a distinct day which 

 they appear to keep to with equal regularity. A curious fact is 

 that another species of Dendrobium (D. criniferum) invariably 

 flowers in Singapore on the day preceding that of D. crwiienatuw, 

 whenever that happens to be. It might be thought that the 

 weather in the district in which the plant was growing was the 

 influencing agent, but this appears to have but little effect on the 

 orchids. On one occasion (Dec. 5, 1<S93J the pigeon orchids 

 developed their flowers so far that they were obviously ready to 

 open them on that day, but an extraordinarily heavy rain retarded 

 them, and the flowers opened the next day, but except in cases like 

 this the weather previous to the flowering does not seem to make 

 any difference to the date of flowering. Some few plants have 

 a regular annual flowering season, such are Calantke curcuh- 

 goides in September, and Grammatophyllum, July and August. 

 A certain number of trees flower only every fifth year, notably 

 the Dipterocarpe<e, Every fifth year there appears to be an 

 average higher temperature, and a period of greater dryness in 

 May or June than in other years, and then and only then is it 

 possible to obtain flowers of these trees. Such trees are most of 

 the Dipterocarpe/v, xantlwphyllum Kunstleri, Careya sp. In this 

 case also all the plants in a given district flower simultaneously. 

 It can easily be understood that it is very important to a plant 

 that all should flower on the same day in order that tbey may be 

 cross-fertilized by the insects that visit them, and this is especially 

 the case in plants in which the flowers last but a single day, as 

 in the case of the Pigeon orchid, but it is difficult to see how 

 this is brought about. A good many trees seem to flower even 

 less often than this and there are not a few which though 

 apparently full grown healthy trees have not given flowers once 

 in ten years. 



Colors oj flowers. 



As is well known the colors of flowers depend to a large 

 extent on the kind of insect fertilizer for which they are destined 

 to prove attractive. The most abundant insects in the thick 

 jungle are the flies (Diptera) and these appear often in enormous 

 abundance when certain trees are in bloom. The Oaks and 



