316 



MICROSCOPIC FORMS OF VEGETABLE LIFE. 



Fig. 106. 



L■,^>il 



with the walls of the cell (Fig. 106, a), but which gradually be- 

 come more isolated, each seeming to acquire a proper cell-wall ; 

 they then begin to move about within the parent cell ; and, when 

 quite mature, they are set free by the rupture of its wall (b), to 

 go forth and form new attachments, and to develope themselves 

 into tubiform cells resembling those from which they sprang, 

 Each of these "motile gonidia" is possessed of only two cilia; 

 their movements are not so powerful as those of the zoospores of 

 Vaucheria ; and they come to an end sooner. This plant forms 

 " resting-spores" also, like those of Vaucheria; and there is every 

 probability that they are generated by a like sexual process. 



They may remain unchanged 

 for a long time in water, when 

 no suitable nidus exists for 

 them; but will quickly ger- 

 minate, if a dead insect or 

 other suitable object be 

 thrown in. One of the most 

 curious forms of this group, 

 is the Hydrodictyon utricula- 

 tum, which is found in fresli- 

 water pools in the midland 

 and southern counties of 

 England. Its frond consists 

 of a green open network of 

 filaments, acquiring, when 

 full grown, a length of from 

 four to six inches, and com- 

 posed of a vast number of 

 cylindrical tubular cells, 

 which attain the length of 

 four lines or more, and ad- 

 here to each other by their 

 rounded extremities, tlie 

 A, dilated exire- points of juuctiou corrcspond- 



tilio.i, a, and coiilaiiiiiig young cells in progress of V & , KUOtS Or mierset 



formation ; — B, conceptacle discharging itself, and tlOnS of the UCtwOrk. Lach 

 setting free young cells, a, 6, c^-c, portion of filament, gf thoSC Cells mav form with- 

 showing the course of the circulation of granular pro- . . , i /. "^ ii* 



topiasm. m itseli an enormous multi- 



tude (from 7000 to 20,000) of 

 "gonidia;" which, at a certain stage of their development, are 

 observed in active motion in its interior ; but of which groups 

 are afterwards formed by their mutual adhesion, that are set 

 free by the dissolution of their envelopes, each group giving 

 origin to a new plant-net. Besides these bodies, however, cer- 

 tain cells produce from 30,000 to 100,000 more minute bodies of 

 longer shape, each furnished with four long cilia and a red spot, 

 which are termed by Braun "microgonidia:" these escape from 

 the cell in a swarm, move freely in the water for some time, and 



Development of Achlya jyrolifei'a: 



