the tentacles seem paralysed, as likewise follows from the action of too strong solutions of certain salts, and by too great heat, whilst weaker solutions of the same salts and a more gentle heat cause movement.  We shall also see in future chapters that various other fluids, some [page 37] vapours, and oxygen (after the plant has been for some time excluded from its action), all induce inflection, and this likewise results from an induced galvanic current.*

* My son Francis, guided by the observations of Dr. Burdon Sanderson on Dionaea, finds that if two needles are inserted into the blade of a leaf of Drosera, the tentacles do not move; but that if similar needles in connection with the secondary coil of a Du Bois inductive apparatus are inserted, the tentacles curve inwards in the course of a few minutes.  My son hopes soon to publish an account of his observations. [page 38]

CHAPTER III.

AGGREGATION OF THE PROTOPLASM WITHIN THE CELLS OF THE TENTACLES.

Nature of the contents of the cells before aggregation—­Various causes which excite aggregation—­The process commences within the glands and travels down the tentacles—­ Description of the aggregated masses and of their spontaneous movements—­Currents of protoplasm along the walls of the cells—­Action of carbonate of ammonia—­The granules in the protoplasm which flows along the walls coalesce with the central masses—­Minuteness of the quantity of carbonate of ammonia causing aggregation—­Action of other salts of ammonia—­Of other substances, organic fluids, &c.—­Of water—­Of heat—­Redissolution of the aggregated masses—­Proximate causes of the aggregation of the protoplasm—­Summary and concluding remarks—­Supplementary observations on aggregation in the roots of plants.

I will here interrupt my account of the movements of the leaves, and describe the phenomenon of aggregation, to which subject I have already alluded.  If the tentacles 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; but this can be seen with much greater distinctness after the process of aggregation has been partly effected than before.  The purple fluid which exudes from a crushed tentacle is somewhat coherent, and does not mingle with the surrounding water; it contains much flocculent or granular matter.  But this matter may have been generated by the cells having been crushed; some degree of aggregation having been thus almost instantly caused. [page 39]