350 BOTANICAL GAZETTE [october 



spores are formed in conditions of greater vegetative activity than 

 gametes, it is reasonable to suppose that the difference between 

 spores and gametes is due to a difference in the activities of the 

 protoplast in the two cases, a difference associated with declining 

 vigor. Under such conditions, the products of metabolism will 

 differ, and substances will be produced that do not appear when 

 the protoplast is in full activity. This means that gametes will con- 

 tain substances that spores do not, and among these substances are 

 those that determine the mutual attraction that results in pairing. 

 If this is true, it follows that different substances differentiate 

 gametes into two kinds that are mutually attractive. These char- 

 acteristic substances which appear later in the vegetative history 

 of protoplasts may be regarded as among the products of wamng 

 metabolism. The appearance of different substances under such 

 conditions is familiar in the case of the autumnal coloration of 

 leaves. 



It does not follow that these substances which characterize 

 gametes appear only when the vegetative vigor of the plant as a 

 whole is declining. This is generally true of such plants as the 

 filamentous algae, but in more complex plants this decline of meta- 

 bolic activity may occur in a region of the plant body, rather than 

 in the body as a whole. For example, it is usually stated that the 

 developing sex organs of mosses check the growth of the axis. It 

 is a fair question to ask whether the sex organs do not appear 

 because for some other reason growth has been checked. A 

 checked growth indicates declining vegetative vigor, and this 

 favors gamete-formation. Another illustration of the same fact 

 may be obtained from the appearance of the sex organs of ferns. 

 When a fern spore germinates, metabolism begins in a relatively 

 feeble way, and during this early period antheridia are formed. 

 Later, when the development of the gametophyte becomes more 

 vigorous, sperm-formation may cease. The so-called "inhibitor 

 of sperms in this case, therefore, is the disappearance of the char- 

 acteristic substances that belong to gametes, on account of the 

 increasing vegetative activity of the protoplasts. In this case only 

 such gametes can be formed as are characterized by a small amount 

 of cytoplasm. Later in the history of the fern gametophyte, after 



