6o8 



LECTURE XXXV 



mence their movements before they are yet free. In dividing Palmellaceaa I have 

 seen the movements begin in the early morning long before the division was finished ; 

 the daughter-cells still hanging together in the middle trembled actively and 

 began to swarm inside the mother - cell. The swarming is no doubt on the 

 whole the same movement as that of the free swimming cells, only restricted by 



the continual impact of the cells 

 one on the other within the confined 

 space of the mother cell-wall. A 

 similar phenomenon exists in the 

 movement of the spermatozoids 

 within their cell-wall, before they 

 break through it. Thuret says of 

 those of the Characege, ' The anthero- 

 zoids are seen to be agitated and 

 to twist in all directions within the 

 segments (cell-segments of the an- 

 theridia) which enclose them ; after 

 several more or less prolonged 

 efforts, they escape to the exterior 

 by a sudden movement, like the 

 elastic rebound of a spring.' In 

 the case of Pelh'a, the Ferns, and 

 Piltilana, according to Hofmeister, 

 the spermatozoid also revolves before 

 it escapes from its cell-membrane. 



The movements of swarm-spores, 

 since they are true vital pheno- 

 mena, only take place between cer- 

 tain limits of temperature, and that 

 an optimum temperature must exist 

 for them at which the maximum 

 of motility occurs, is only a special 

 case of what was stated generally 

 in Lecture XII: I shall therefore 

 not go further into that matter. 

 The irritability of swarm-spores for 

 light, however, belongs not only to 

 the most remarkable phenomena of 

 irritability in the vegetable king- 

 dom, but also, from the most 

 recent investigations of Stahl and 

 Strasburger, to those best known. 

 Before giving the most important results, however, I have still to mention a 

 fact which comes of necessity into consideration here, and which was established 

 by me about six years ago : this concerns the purely passive movements which 

 the swarm-spores undergo under certain circumstances, simply from currents in 



F'g- 35^5 — 'Warm-cliamber for the examination with the microscope 

 of the movements of protoplasmic structures at different and constant 

 temperatures. The chamber is constructed of zinc, and possesses double 

 walls below and at the four sides, the space between being filled with 

 water ; it is open above to facilitate the insertion of the microscope m, 

 the fine adjustment-screw of which appears at s; dd lid; / window 

 which takes coloured or colourless glass ; / thermometer. 



