THE SENSES OF PLANTS. 289 



by a good number of aerial roots. At present the 

 board is hung against the trunk of a small tree, its 

 back being in actual contact. To all appearance 

 it is yet fairly sound although decay has probably 

 set in, and it will be rotten in a year or two. 

 Three months ago we noticed that the orchid was 

 hanging over as if detached, and on examination 

 found it had loosened itself as far as it could and 

 was only supported by the wire. Looking closer 

 again we discovered that it had thrown out several 

 new roots which clasped the tree, and was prepared 

 to swing itself from the one support to the other, 

 had not the wire kept it back. In the forest no 

 doubt such migrations are common the branch 

 becomes rotten, the orchid throws out extensions 

 in every direction to search for something better, 

 some of these attach themselves to a living bough, 

 perhaps several feet distant, and the whole plant is 

 moving off before its weak perch gives way. What 

 is specially noticeable is the fact that it does not 

 wait for the downfall, but "takes time by the fore- 

 lock." In the case of the Burlingtonia it is notice- 

 able that the aerial root which encircles the tree is 

 much longer than any other that it produced while 

 in its old position, and is evidently thus developed 

 for a special purpose. 



In many orchids, especially those of a large size, 

 19 



