i9Hl COULTER— REPRODUCTION IN PLANTS 339 



escapes into the surrounding medium. The escaped protoplast 

 (spore) is nothing more than a protoplast acting independently 

 of its wall and of its parent plant. No new powers seem to belong 

 to the escaped protoplast; it begins a series of divisions, but being 

 free from the parent form, the divisions result in a new individual. 

 The difference between such a spore, therefore, and any other proto- 

 plast belonging to the parent body is not a difference of power but 

 of opportunity. 



Ordinarily the spore-forming protoplast begins a series of 

 divisions before escape, resulting in several spores; but it is obvious 

 that the series of cell divisions is responsible for reproduction, 

 whether the protoplast divides before it escapes, or escapes before 

 it divides. In many fungi the detachment of spores is secured, not 

 by the discharge of protoplasts, but by the abstriction of walled 

 cells from special branches. This "pinching off" a part of the 

 body is merely a detail of separation. The essential fact is that 

 a spore means a protoplast separated from one individual, and 

 capable of producing another individual. The multitude of names 

 applied to spores on the basis of secondary characters has obscured 

 the fundamental idea that belongs to all of them, the idea of a 

 detached protoplast. 



It would be interesting to know what conditions determine the 

 separation of a protoplast from its wall and its abandonment of 

 the structure it has made and kept in condition. A possible sug- 

 gestion may be obtained from the occasional behavior of proto- 

 plasts at the inception of conditions unfavorable to vegetative 

 activity. Just as in spore-formation, the protoplasts become 

 freed from the wall, round off, and are entirely detached from the 

 general life of the individual which has produced them. The 

 experimental control of spore-formation in many algae and fungi 

 shows that conditions can be supplied which inhibit spore-formation 

 indefinitely, and other conditions can be supplied which stimulate 

 abundant spore-formation. In general, whatever diminishes vege- 

 tative activity favors spore-formation, so that it is the physiological 

 condition of the protoplast that determines whether it continues 

 to do vegetative work, or becomes a spore. It is certainly sug- 

 gested that the favorable condition for spore-formation in nature 



