90 ROMANCE OF LOW LIFE AMONGST PLANTS. 



when the first individuals were brought from some 

 unknown rocks by the currents of the ocean." ^ 



Active Zoospores. 



No phenomenon in the cycle of plant life, as 

 exhibited in its lower forms, is more instructive 

 and sueeestive than the movements of the sexual 

 elements in some of the thread-like fresh-water Alga?, 

 and especially those which bear the generic name of 

 Qi,dogonmm. In their simple and sterile condition, 

 these Algae consist of cylindrical threads, divided by 

 transverse partitions into elongated cells. Whilst 

 growing and vigorous these cells contain a green 

 colouring matter, which imparts its colour to the 

 threads, but in the course of time these contents are 

 absorbed in the formation of the organs which are 

 developed at their expense within the cells. In one 

 scries of species the little male plants are produced 

 from other cells of the same thread as those which 

 are converted into female cells. In another scries 

 the male plants are produced within threads distinct 

 from those which develop female cells, so that some 

 of the threads produce only female cells, and others 

 only the male. Of the first scries an example may 

 be taken when in its mature condition, and then it 

 will be observed that the threads are no longer of 

 equal thickness throughout, but are swollen in some 

 places to double their original diameter, in an abrupt 

 and bladder-like manner, the inflations having a 

 somewhat globose or elliptical form. The cells thus 

 inflated are the vital female cells, which are termed 

 » W. II. Harvey, "Nereis Boreali-Americana," p. 53. (1S51.) 



