14j2 Ais^ atomy and phybiologt of 



walls of the individual cells, either the side becoming concave in 

 the motion xmdergoing abbreviation, or the opposite side expand- 

 ing. The locomotion of the entire filament is influenced in the 

 same way as that of the Diatomaceae and Desmidiacese by illumi- 

 nation or drying np of the mud, and the movement from a dark 

 towards an illuminated place, is, in particular, very distinct (Du- 

 trochet, '^Memoires/' i 112). 



Ohserv. This is, of course, not the place to enter into the much con- 

 tested question whether these beings are actually plants, and not rather 

 animals. The former is^ as I at least believe, incontestibly proved by 

 Kiitzing ("Die Kieselschaaligen JBaclllarien'^), E^alfa (''British Desmidiece,'') 

 and others. But it deserves mention that the contraction into a spiral 

 form occurs not nnfrequently in still higher degree than in the OsciUa- 

 toriece, in most undoubted plants, namely, the Zygnemece (See Meyen, 

 '' Fhydohgie^^ iii. 5%Q). 



Rapid advancing and retreating movements, like those the 

 lower Algae exhibit, are unknown in those organs of higher 

 plants, consisting of a single cell or row of cells, which might, in 

 reference to their structure, be compared with the plants above 

 referred to, yet we find in such simply constructed organs, pheno- 

 mena of curvation which are indeed most closely connected with 

 their growth, but may possibly be brought into connection, in 

 many respects, with the phenomena of motion. I include among 

 these the phenomenon, that many filifoim cellular processes 

 grow in a definite direction, and attach themselves upon foreign 

 bodies. 



The pollen-tubes are, above all, to be recalled to mind here, 

 curving, as they do, after their exit from the pollen-grain, to come 

 in contact with the hairs of the stigma, applying themselves upon 

 these, and penetrating into the conducting tissue of the style. 

 This phenomenon has often been compared with germination, and 

 correctly, for in that curvature, in the penetration of the pollen- 

 tube into the conducting tissue, we meet with the same pheno- 

 mena, only in a more simply organized part, as in the radicle of a 

 germinating plant. Still greater is the analogy with the radicles 

 of many Cryptogamia, whether these are protrusions of single cells, 

 as in many Gon^ervm and in the Liverworts, or simple rows of cells, 

 as in the Mosses. In these capillary roots we find the same ten- 

 dency to grow downwards, and the same adherence to foreign 

 bodies. One might be inclined to seek the cause of this curvature 

 of the cells, and their adherence to foreign bodies, in a retardation 

 of the growth of those parts of the cell-membrane which come in 

 contact with the foreign bodies, behind that of the free parts of 

 the membrane. But it is possible that the conditions are far more 

 complicated. For if we compare these phenomena with the pro- 

 cesses which are presented to us in the compound organs of the 

 higher plants, we find in the movements of these capillary organs, 

 corresponding processes to those which, in the higher plants, are 



