60 Irritability observed in the Stems of Plants, 



the stem was removed, and a longitudinal section made in 

 the truncated portion : no perceptible divergence ensued. 



5. The piece of stem used in the last experiment was 

 placed in distilled water. In six hours the divided portions 

 had separated to the extent of half an inch. On being removed, 

 and immersed in syrup, the divergence gradually decreased, 

 precisely as in the case of the stem which had not been sub- 

 mitted to the deleterious influence of a poisonous agent. 



6. Above 2 in. of the stem of Stachys palustris, removed at 

 about 3 in. from its root, was left for some days on a glass 

 plate exposed to the air. From the evaporation of its 

 moisture, it withered, and, in a short time, became nearly dry. 

 In this state, no one would hesitate to pronounce the portion 

 of stem to be quite dead, or, at least, pretty well deprived of 

 any thing approaching to vital irritability. A small piece of 

 this dead stem was removed, and a longitudinal section made 

 in its upper portion ; but not the slightest appearance of di- 

 vergence ensued. 



7. The remaining portion of the dried stem of the Stachys 

 was placed in a weak syrup. In twelve hours it had absorbed 

 a considerable quantity (? by capillary influence), and nearly 

 regained its natural state of turgescence. A longitudinal 

 incision was then made in its upper portion : diiwgencc im- 

 mediately ensued ; and, on being immersed in water, the seg- 

 ments separated, and became curved as in experiment 2. 



The above experiments were repeated with the stems and 

 petioles of different herbaceous plants, and with similar re- 

 sults. Let us now see what deductions can be fairly drawn 

 from them. That the property of divergence does not depend 

 upon " vital irritability," as assumed by its discoverer, is 

 shown by experiments 5. and 7., in which the property was 

 restored, by artificial means, to stems deprived of vital in- 

 fluence, by being isolated from the plants bearing them, and 

 submitted to the deleterious influence of a poison, or to 

 desiccation. Finding that vital influence alone is insufficient 

 to explain the cause of the phenomenon under consideration, 

 we are compelled to have recourse to some physical agent. 

 That this agent cannot be "elasticity " the observations of Dr. 

 H. Johnson (op. sup. citat.) are more than sufficient to de- 

 monstrate, seeing that the property of divergence is absent in 

 the most elastic parts of plants, as true woody fibre, rattan 

 cane, Sic. ; and present in the most delicate herbaceous plants, 

 as well as in the most inelastic ; as in the individuals of the 

 family Thymelaceae. As, then, physical elasticity fails to 

 explain the nature of divergence, we must seek for another 

 more satisfactory cause; and this, I think, we shall find in 



