94 ON THE PLANT- CELL. 



In Najas major and Caulinia fragilis, in the fruit-stalk of the Junger- 

 manniacce (according toMeyen), the motions are precisely of the same kind. 

 The observation is of extreme difficulty in Stratiotes aloides; and after 

 frequently repeated examination of every species of Potamogeton, I have 

 only twice succeeded in actually seeing the motion : I have, unfortunately, 

 forgotten to note the species. 



After the most careful research with the best instruments, I have 

 been unable to perceive a trace of the presence of vibratile cilia as a 

 cause of the motion, and it is very improbable that such should exist. 

 Whenever these cilia are found in animals and plants, they always 

 appear as processes on the exterior, never in the interior, of cells. 



This kind of circulation, taken as a whole, seems to be, for the most 

 part, a phenomenon wholly peculiar to the vegetable-cell, and to be con- 

 nected with its perfect individuality. All the plants above mentioned, 

 in which the circulation is observed with certainty, are aquatic, or else 

 very fond of water, belonging to families very low in the scale of 

 organisation, in which the cells exhibit a great degree of independence, 

 so that separated portions of the plant (for instance, of the leaves of 

 Vallisneria) often retain their vitality for months. The supposed circu- 

 lation of the same kind in higher terrestrial plants I must for the present 

 leave undetermined, as I have never been successful in making even a 

 single observation with regard to it. 



Historical and Critical In the year 1772, Bonaventura Corti dis- 

 covered the circulation of the sap in certain Characece and in Caulinia 

 fragilis (" mia pianta," as he constantly terms it), and also extended his 

 observations to many land and water plants, the determination of which 

 is, at the present time, for the most part impossible. Fontana confirmed 

 these discoveries, and at the same time cleared up some errors into which 

 Corti had at first fallen. Both these inquirers had observed so accu- 

 rately, and made such numerous experiments, that their successors were 

 not able to add anything essential. Their discoveries, however, in 

 the times of the Linnaean school of compilers, were so totally forgotten, 

 that C. L. Treviranus, first in 1807, rediscovered the motion of the sap 

 in the Charce, and Amici in 1819 in Caulinia; to which instances Meyen 

 subsequently added the other plants enumerated, after Horkel had again 

 fallen upon the writings of Corti, and drawn attention to their contents. 



Corti's observations, above alluded to, upon land plants, as has been 

 said, do not admit of repetition. Meyen* formerly said a good deal 

 about these observations, that he had confirmed them all, without at the 

 same time entering into particulars, with reference to which I would 

 remark, that at the time he wrote his " Phytotomie " he was unac- 

 quainted with the kind of motion described in the following section, or, 

 at all events, did not distinguish it from the other. In his last work f he 

 passes it over in, as it appears, prudent silence. In his "Prize Essay" 

 he states that he has also observed the motion in Pistia Stratiotes. He 

 and others have repeatedly confounded the circulation here described 

 with the following. 



Corti's notion, which was opposed even by Fontana, that the ascending 

 and descending streams are separated by a septum in the cell, has been 

 repeatedly broached since his time, but it is easily shown to be false. 



* Meyen, Phytotomie, S. 182. Ueber die neuesten Fortschritte der Anatomie und 

 Physiologic. Harlemer Preisschrift, 1836, p. 165, and elsewhere, 

 f Physiologic, vol. ii. p. 206, et seq. 



