206 



THE AMEEICAN MONTHLY 



[November, 



have likewise observed the nature of 

 the gonidial layer, then carefully 

 group the outer features of the plant. 

 As well as a mark of carefulness, it is 

 a good disciplinary process to write 

 down all the points in examination as 

 you go on, both internally and exter- 

 nally ; and, when this is complete, 

 turn to the Manual and look for a 

 description of your plant, under that 

 family, series, tribe, or sub-tribe, to 

 which you have already concluded it 

 belongs. Drawings of the spores, or 

 any part of the plants, should be at- 

 tached to the sheets upon which they 

 are mounted, and the whole be arran- 

 ged together in the herbarium, ac- 

 cording to their classification. Mi- 

 croscopic slides, neatly mounted and 

 finished, illustrating different plants, 

 are very useful for reference and in- 

 struction. 



The Lichen-herbarium is usually 

 made up according to the taste and 

 convenience of the parties concerned. 

 Leighton describes his in his Lichen- 

 Flora. If it is intended that the her- 

 barium shall follow the order of the 

 system of classification, then the best 

 way is to mount each species and 

 form, upon a separate sheet of car- 

 tridge paper, cut to a convenient size, 

 and in due order arrange so many to- 

 gether, in suitable covers, upon the 

 herbarium shelves. Thus, as fresh or 

 new species come, they can be insert- 

 ed in their proper places. 



The Lichen-Flora of Great Britain, 

 at present, comprises upwards of 1700 

 species, forms, and varieties ; and un- 

 doubtedly, there are yet many new 

 species to discover. Here then, is a 

 wide field for activity and enterprise ; 

 and we can promise that it is as full 

 of delight and interest as it is wide. 

 But, the morphology, chemical nature, 

 and the relation of Lichens to the 

 atmospheric medium, are yet to in- 

 vestigate. Researches in these de- 

 partments have been begun, but that 

 is all. These deeper subjects of study 

 though, can only present themselves 

 properly to the mind of the student, 

 when he has mastered the primary 



elements, and learned readily to dis- 

 tinguish one plant fron another. 



Motion of Diatoms. 



The notes on motion of Diatoms 

 published in the April number of this 

 Journal have called out some state- 

 ments as to similar phenomena noticed 

 by other observers. Among these, 

 few will be found so deserving of 

 consideration as those of Dr. G. C. 

 Wallich, of London, formerly Sur- 

 geon-Major in the British India Ser- 

 vice. Dr. Wallich is a recognized 

 authority in regard to the natural 

 history of the Protozoa as well as the 

 Diatomaceae, and his observations in 

 both hemispheres are important 

 contributions to science. Several of 

 his articles are noteworthy for their 

 bearing on the subject of the motive 

 power of diatoms, and v/e are sure the 

 readers of this Journal will be thank- 

 ful for references to them. 



In the Anfials and Magazine of 

 Natural History for January, i860, 

 the latter part of a paper on the dis- 

 tribution, etc., of the free-floating Dia- 

 tomacese is devoted to the considera- 

 tion of the motive powers of these 

 organisms, maintaining that the 

 motion cannot be due to osmotic 

 forces, but must be ascribed to " the 

 " existence of prehensile filaments, 

 " capable of alternate extension and 

 " retraction, of extreme tenuity, yet of 

 " extraordinary strength and elasti- 

 " city," in virtue of which both the 

 ordinary to-and-fro movements of the 

 diatom-frustule itself, and the motions 

 imparted by it to neighboring extrane- 

 ous particles or masses of matter are 

 brought about. 



Similar views were advanced and 

 supported by Dr. Wallich in a paper 

 read before the Royal Microscopical 

 Society, in December, 1859, and sub- 

 sequently published in the Quarterly 

 Journal of Microscopical Science. 

 This had special reference to the 

 views of Professor W. Smith on the 

 subject, as stated in his " Synopsis of 

 British Diatomaceae." 



