40° BOTANICAL GAZETTE [JULY 
These views are opposed (rightly, it seems to me) by Lau- 
terborn,3 who affirms that such an arrangement as supposed by 
O. Miller could not impart motion to the cell. 
I cannot go into the details of all the observations quoted pro 
and contra for each of these hypotheses, but if I can trust in my 
own observations, I am obliged to sustain the theory of osmotic 
currents. I have been very often in position to observe the 
movements of these organisms, either incidentally or with pur- 
pose, and I have never met with facts which could be advanced 
against the osmotic hypothesis. 
These observations give me the conviction: 
1. That the objection that movements are possible only ina 
definite position of the cell with respect to the glass (which is 
considered as the substratum) rests upon inexact observations. 
Many times I have seen cells of Diatomacez executing their 
progressive movements as well in the frontal as in the lateral 
position. It is possible that various species behave differently 
in this line; but in very many of them, and especially in 
those symmetrical Naviculacee and Nitzschiex, the position 
of the cell does not influence the movement. It is stopped 
sometimes by the sudden change of position in consequence 
of a shock, which may be easily explained by the rigor which 
generally follows such treatment of the protoplasm. 
2. Nor do I think the affirmation exact that contact with the 
glass is essential to movements.s So far as my own experience 
reaches, I observed on the contrary that such contact is an 
impediment to the movement and perhaps is the cause of the 
transformation of free swimming (gliding) of the cell into creep- 
ing. The impediment is found partly in the friction, partly in 
the sticking of the mucus surrounding the cell membrane to the 
3Zur Frage nach der Ortsbewegungen der Diatomaceen. Ber. d. D. Bot. Ges. 12: 
73. 1894. 
4 This observation is in accord with that of O. Miiller, that the position towards 
the substratum does not influence the movement in Pinnudaria, Stauroneis Phoenicen- 
tron, and Nitzschia sigmoidea, 
5 The same objection is stated by O. Miiller, who observed the movements of the 
algz in a drop of water suspended from a cover glass 
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