12 INTRODUCTION. 



So extraordinary were the statements from time to time 

 put forth relative to the spontaneous motion of the reproduc- 

 tive germs of many Alga a class of productions always re- 

 garded as vegetable considered to be, that many observers, 

 and some do even now, refuse to give their belief to their 

 accuracy. So numerous are the observers who have witnessed 

 the singular motions above recorded, that the facts announced 

 in reference to them must be regarded as amongst those 

 which ought to be generally received and adopted. For a 

 long time I myself doubted the reality of the existence of 

 zoospores ; I have now satisfied myself on this head, having 

 repeatedly witnessed their movements in very many Conferva, 

 but never as yet in any species belonging to the conjugative 

 tribe of Alga ; in which, however, Agardh declares himself 

 to have witnessed it. For extended observations on the 

 motion of the zoospores of the Alga, see, in " Annalcs des 

 Sciences Naturelles (Botanique), 1836," a memoir " Sur la 

 Propagation des Algues. Par J. G. Agardh. Extrait." 



It is surprising that, out of the number of those 

 who now study the Alga, so few should have witnessed 

 the singular motion of the zoospores. The spring is the 

 best season for observing these bodies. If, at that time, 

 a number of Alga, collected indiscriminately from different 

 localities, are placed in a vessel of water over-night, and 

 allowed to remain undisturbed until the morning, usually 

 there will be noticed on the surface of the water a thin 

 green pellicle or scum: this, when examined, will be found 

 to consist of the zoospores of different species of Conferva, 

 in all possible stages of developement. Their motion is 

 most active early in the morning; and they would appear 

 to shun the light, as they are generally met with on the 

 side of the vessel farthest removed therefrom. 



Next in interest to the discovery of the zoospores them- 

 selves, and for which science was mainly indebted to the 

 researches of J. G. Agardh, is that of the means by which 

 their motion is effected. J. G. Agardh declared that it 

 depended upon the movement of a prolongation or beak, 

 with which each zoospore was said to be furnished ; others 



