6o6 LECTURE XXXV. 



which is discharged through the air from a rifled barrel. Naegeli seems to have been 

 the first not only to exactly study the motion of swarm-spores, but also to criticise 

 them from the physical and mechanical point of view. It may therefore be of service 

 to the reader to be made acquainted with his exact expressions as to the apparent 

 and true velocity in the progressive movement of swarm-spores. 



' The movement of swarm-cells,' says Naegeli ^ ' is usually described as very 

 active, and the rapidity with which they bustle about is no trivial reason for their 

 having been designated animals. In this it has often been forgotten that one is 

 looking through the lenses of the microscope, and that the swarm-cells are in 

 reality much less active than they appear to be. When we observe them with a 

 power of 300 diameters, it is not only that the cells appear to us 300 times 

 larger, but the motion also appears 300 times more rapid, since the space 

 traversed in a given time is in- fact also increased under the microscope 300 

 fold. In a watch laid under the microscope, with a power of 100 diameters we 

 see the apex of the long hand engaged in fairly rapid trembling and jerking move- 

 ments, while the apex of the short hand proceeds extremely slowly, the movement 

 scarcely perceptible. I observed the slowest continuous movement of the cell 

 contents in Char a when the temperature of the water was i°C., the most rapid 

 in the same plant when the temperature of the water was 37°C. The length of 

 one foot, if the motion is calculated to that measure, would be passed over in 

 the first case in fifty hours, in the second case in thirty minutes. Diatomacege 

 at the ordinary temperature of the laboratory traverse one foot in 14-21 hours; 

 they thus move about six times more slowly than the apex of the long hand of a 

 watch. Swarrn-cells take mostly about one hour, the most rapid only a quarter 

 of an hour to pass over a distance of one foot. The most nimble equal in their 

 movements the apex of the long hand of a clock, the face of which has a 

 diameter of one foot and a-quarter, and would be left far behind by the laziest of 

 snails^. Without magnification, even if the little plants were quite visible, their 

 movement would not be seen, on account of its slowness. — The Infusoria move 

 but little faster than the vegetable cells. Instead of the active animal movement 

 of the latter, it would be more correct to speak of the slow plant-like movement 

 of the former. 



' Whether the movement of a body appears to us rapid or slow, however, 

 depends also on the relation between its size and the space passed over in a 

 definite time. If an elephant and a mouse traverse an equal distance in the 

 same time, we call the first slow, the second quick. A man in walking passes 

 over somewhat more than half his length in one second. The most rapid swarm- 

 cell traverses in the same time a distance which is two and a half times as great as its 

 diameter; the Diatomacege only the one-tenth part of their length, and short fila- 

 ments of Oscillatoria merely the one-hundredth part of their length, longer ones 

 much less.' 



According to Naegeli, swarm-cells have three forms of movement; in many 



1 Naegeli, 'Die Bewegung im Pflanzenreich^ in his ' Beitr. zur wissensch. Bot.,' Heft. 2, i860, 



P- 13- 



^ The movement of swarm-spores is thus slower than that of a particle of combined water and 

 lithium which ascends in the wood during active transpiration. 



