AND IRRITABILITY OF SENSITIVE PLANTS 223 



as much as possible to the chemical reagents that are applied. To 

 such preparations chemicals were added and the results observed carefully 

 under the microscope. 



When concentrated hydrochloric acid is added to sections con- 

 taining crystals, it is noted that the crystals dissolve gradually. Con- 

 glomerate crystals dissolve more readily than the prismatic forms. 



In the solution process the conglomerates are broken up into the 

 small prisms of which each crystal is composed, and these particles 

 are then dissolved. Each of the rhombohedral crystals in the solution 

 action of the acid is divided into two segments, the division taking 

 place along the partition line across the middle of the crystal. This 

 seems to indicate that this line is different in resistance to the rest of 

 the crystal, and may even consist of a different substance. Complete 

 solution of the crystals usually takes place in 1-3 minutes. Crystals 

 separated from the mucilaginous sheaths in which they are enveloped 

 are dissolved in a shorter time, the sheaths retarding the solution action. 



Concentrated nitric acid acts like concentrated hydrochloric but 

 dissolves the crystals in a slightly shorter time. The crystals are like- 

 wise soluble in concentrated sulphuric acid, concentrated caustic potash, 

 but insoluble in acetic acid. 



Aggregation 



Darwin (12, p. 38) in his extensive studies on Drosera rotundifolia 

 observed that a very interesting change takes place in the appearance 

 of the contents of tentacular cells when stimuH are applied to the irrito- 

 contractile tentacles. "If the tentacle of a young, yet fully matured, 

 leaf that has never been excited or become inflected be examined, the 

 cells forming the pedicels are seen to be filled with homogeneous, purple 

 fluid. The walls are lined by a layer of colourless circulating protoplasm. 

 If a tentacle is examined some hours after the gland has been excited 

 by repeated touches, or by an inorganic or organic particle placed on 

 it, or by the absorption of certain fluids, it presents a wholly changed 

 appearance. The cells, instead of being filled with homogeneous purple 

 fluid, now contain variously shaped masses of purple matter, suspended 

 in a colourless or almost colourless fluid." Darwin described the 

 phenomenon as an aggregation process, and the masses formed are 

 "aggregation bodies." The shapes of these masses are fully described 

 in Darwin's "Insectivorous Plants". 



De Vries (14, p. 6) made additional researches on the aggregation 

 phenomena in Drosera rotundifolia, and distinguished three phases in 

 agregation— (1) Retarded and much more clearly differentiated circula- 



