10 76 



Proceedings of the Royal Irish Academy. 



For the testing of the more rapidly falling seeds — those of many 

 powder-seeded species, for instance — a much longer fall, amounting to forty 

 feet, was given, to ensure more accurate results, and also because in these 

 cases acceleration due to gravity extends over an appreciable period. For 

 this purpose, one of the stairways at the Eoyal College of Science for Ireland 

 was utilized. 1 



In the following lists, the actual times taken to fall the distances 

 measured are recorded, since, in the case of many even of the smallest seeds 

 destitute of appendages, acceleration is undoubtedly no negligible factor (as it 

 is with the more efficient plume and wing seeds), and, in consequence, we 

 are not dealing with a uniform rate of fall, and cannot deduce the time taken 

 to fall oue distance from the time taken to fall another. 2 



Plume Seeds. 

 Time taken to fall twelve feet. 



Banunculaceae- 

 Leguminosae— 

 kosaceae — 

 Onagraceae — 



COMPOSITAE — 



Seconds 



Clematis Vitalba, 5 '4 



Trifolium arvense, 5'0 



Dryas octopetala, 6 '5 



Epilobium hirsutum, 19'0 



E. montanum, 20'0 



E. palustre, 237 



Eupatorium cannabinum, 16 - 

 Aster Tripolium, 8 - 



Solidago Virgaurea, 7 -l 7 



Erigeron acre, 8'8 



Inula salicina, 13"5 



I. crithmoides, 4' 5 



Pulicaria dysenterica, 10 - 



Senecio vulgaris, 12'8 



S. sylvaticus, 17'3 



S. Jacobaea, 10 - 



Carlina vulgaris, 4 - 5 



Carduus pycnocephalus, 5'0 



Cnicus lanceolatus, 12 - 4 



1 1 have to Uiank Mr. John Adams, m.a., for kind assistance in this latter series of experiments. 



2 To convert the figures in the following lists into miles per hour (approximately), invert them 

 and multiply hy 8 where a 12-foot fall is referred to, or by 27 for a 40-foot fall. The result will be 

 almost correct for slow-lallmg seeds; but for fast-falling seeds the results will be too small, since the 

 figures in the list represent something less than the terminal velocity of fall. 



