VOL. LXXVIII.] PHILOSOPHICAL TRANSACTIONS. 423 



similar phaenomenon has been observed, where indeed an obvious botanical 

 analogy would lead one to expect it, in the Drosera. See Dr. Withering's Bo- 

 tanical Arrangement of British Plants. All these movements are, I think, cer- 

 tainly to be attributed to irritability. We must be careful not to confound them 

 with other movements which, however wonderful at first sight, are to be ex- 

 plained merely on mechanical principles. The stamina of the Parietaria, for 

 instance, are held in such a constrained curved position by the leaves of the 

 calyx, that as soon as the latter become fully expanded, or are by any means re- 

 moved, the stamina, being very elastic, fly up, and throw their pollen about 

 with great force. I have lately observed a similar circumstance in the flowers of 

 Medicago falcata. In this plant the organs of generation are held in a straight 

 position by the carina of the flower, notwithstanding the strong tendency of the 

 infant germen to assume its proper falcated form. At length, when the germen 

 becomes stronger, and the carina more open, it obtains its liberty by a sudden 

 spring, in consequence of which the pollen is plentifully scattered about the 

 stigma. The germen may at pleasure be set at liberty by nipping the flower so 

 as gently to open the carina, and the same effect will be produced. 



As the foregoing experiments show vegetables to possess irritability in common 

 with animals, so there are plants which seem to be endued with a kind of spon- 

 taneous motion. Linnaeus having observed that the rue moves one of its stamina 

 every day to the pistillum, I examined the Ruta chalepensis, which differs very 

 little from the common rue, and found many of the stamina in the position 

 which he describes, holding their antherae over the stigma; while those which 

 had not yet come to the stigma were laying back upon the petals, as well as 

 those which, having already performed their office, had returned to their original 

 situation. Trying with a quill to stimulate the stamina, I found them all quite 

 devoid of irritability. They are stout, strong, conical bodies, and cannot, with- 

 out breaking, be forced out of the position in which they happen to be. The 

 same phaenomenon has been observed in several other flowers; but it is no 

 where more striking or more easily examined than in the rue. 



1 could wish to find an instance of this spontaneous motion combined with 

 irritability in one and the same plant; but I confess I do not know one. From 

 analogy I should think it not impossible that the Dionaea muscipula, and perhaps 

 the Droserae, may have the same motion in their stamina as the Ruta, Parnassia, 

 and Saxifraga, while their leaves possess irritability. But if this be the case, the 

 seats of these 2 properties, being so different and remote from each other, should 

 seem to have as little connection as if in 2 different plants. There still remains 

 then this difference between animals and vegetables, that though some of the 

 latter possess irritability, and others spontaneous motion, even in a superior de- 

 gree to many of the former, yet those properties have hitherto in animals only 



