ON THE STRUCTURE OF OSCILLATORIiE. 257 



Asa general rule, motion, no doubt, is one of the best 

 zoognomic characters, considering that the generality of plants 

 are fixed and rooted to the soil. The idea of focomotion, with 

 regard to land plants, would therefore involve an absurdity, 

 and the motions which have been observed in them, and of 

 which some striking instances have been mentioned, must be 

 necessarily confined to their several parts. Under altered 

 external conditions of vegetable existence, however, the case 

 is different. Amongst aquatic plants, those with roots stand, 

 of course, in the same category as land plants ; others, without 

 roots, are kept floating on the surface of the water by the 

 construction of their leaves or other contrivances, as air-vessels 

 (aerocysta?) for instance, such a provision being sufficient for 

 maintaining their individual existence intact. With regard to 

 those minute and beautiful objects, however, which are com- 

 prised under the general name Microscopic plants, quite 

 different relations obtain, and what in the former class of 

 plants must be regarded as a superfluity, we must here postu- 

 late as an indispensable requirement for their preservation, 

 nay, their very existence. Take, for instance, the Diatomacece 

 or Desmidie(e. Light is as indispensable to them as to the 

 generality of plants, or as the air to us. This is an indis- 

 putable fact. Now, fi'om their very minuteness, and the 

 nature of the locality where they dwell, they are every moment 

 exposed to be buried beneath the mud, and myriads are thus 

 buried by every rising wave ; they must inevitably perish if 

 not accidentally disentombed ; but a bountiful Nature has left 

 nothing to accident as regards the preservation of her offspring, 

 and even in this instance her own ample resources have not been 

 withheld, for she has provided them Avith an ingenious loco- 

 motive apparatus, which is to them what wings are to birds 

 — these, deprived of their wings, would certainly die of 

 hunger, setting aside that they would be left without the means 

 of escape from their natural enemies, — the others, without 

 their power of motion, would perish for want of the quick- 

 ening rays of light. Thus the presence of cilia, as organs 

 of locomotion, was recognised in several undoubted vegetable 

 organisms, which in their play had apparently so much of a 

 spontaneous character, that it became necessary to alter the 

 old formula, and v. Siebold stated that motion could only be 

 regarded as a proof of animality, if it consisted in, or was 

 accompanied by, voluntary contractions of the body. This 

 was done in order to exclude the moving spores of Algol from 

 the class of animals ; but, more recently, other instances have 

 been brought forward which necessitate a further modification 

 of this formula, and the mistake of relying for our classifica- 



