is a general stream up one side of the hair anxl down the otlier. 

 But this does not prevent the existence of partial currents which 

 take different routes; and, sometimes, trains of granules niav be 

 seen coursing swiftly in opposite directions, Avithin a twenty- 

 thousandth of an inch of one another; while, occasionally, oppo- 

 site streams come into direct collision, and, after a longer or 

 shorter struggle, one predominates. The cause of these currents 

 seem to lie in contractions of the protoplasm wliicli bounds the 

 channels in which they flow, but wdiicli are so minute that the 

 best microscopes show only their effects, and not themselves. 



The spectacle afforded by the wonderful energies prisoned 

 within the compass of the jnicroscopic hair of a plant, which we 

 commonly regard as^ mei^y passive organism, is not easily for- 

 gotten by one who has watched its display continued hour after 

 hour, without pause or sign of w^eakening. The possible com- 

 plexity of many other organic forms, seemingly as simple as the 

 protaplasm of the nettle, dawns upon one ; and the comparison of 

 such a protoplasm to a body with an internal circulation, which 

 has been put forward by an eminent physiologist, loses much of 

 its startling character. Currents similar to those of tlie hairs of 

 the nettle have been observed in a great midtitude of very dif- 

 ferent plants, and weighty authorities have suggested that they 

 probably occur, in more or less perfection, in all young vegetable 

 cells. If such be the case, the wonderful noonday silence of a 

 tropical forest is, after all, due only to tlie dullness of our hear- 

 ing ; and could our ears catch the murmur of these tiny mael- 

 stroms, as they whirl in the innumerable myriads of living cells 

 which constitute each tree, wo should be stunned, as with the roar 

 of a great city. 



Among the lower plants, it is the rule rather than tlie ex- 

 ception, that contractility should be still more openly manifested 

 at some periods of their existence. The protoplasm of Algce and 

 Fungi becomes, mider nniny circumstances, partially, or com- 

 pletely, freed from its woody case, and exhibits movements of its 

 whole mass, or is proju'lled by the contractility of one, or more, 

 hair-like prolongations of its body, Avliich are called vibratile cilia. 

 And, so far as the conditions of the manifestation of the phenom- 

 ena of contractility have yet been studied, they are the sani^ Jbr 

 the plant as for the animal. Heat .md electric shocks influence 

 both, and in the same Avay, though it ma) be in different degrees. 

 It is by no means my intention to suggest that there is no differ- 



