252 LIFE HISTORY OF BRYOPHYTA 



ever, as soon as conditions are favorable the sexual organs and 

 gemetes will appear. There are several features in this historv 

 that must be kept clearly in mind. In the first place, the gameto- 

 spore is not discharged from the plant as in the case of the green 

 or brown algae, but remains permanently in the archegonium, 

 where it continues to be nourished by the plant during its germi- 

 nation and the formation of its spores. Therefore, it develops 

 essentially as a parasite upon the plant, as is the case among the 

 red algae. This retention and nourishment of the germinating 

 gametospore in the plant is perhaps the most important of all 

 the variations that appear in plant life. Owing to this relation- 

 ship the gametospore attains a larger growth with increased 

 power of spore production. In this way the development of 

 many new plants is made possible by a single fusion of gametes. 

 This is a very significant feature in terrestrial plants, since the 

 fusion of the gametes is effected with more difficulty, owing to 

 the absence of aquatic conditions. Without doubt this change 

 was induced bv the transference of foods from the sexual to the 

 asexual plant derived from the gametospore. This loss of food 

 gradually prevented the sexual plant from producing spores or 

 other bodies designed to multiply its numbers and we will finally 

 see that the sole work of the sexual plant is limited to the pro- 

 duction of gametes. Note also that the gametespore not only 

 has a larger growth but a longer life. This is of the utmost im- 

 portance because it became exposed in this way to a new series 

 of stimuli that affected it profoundly and that resulted in the 

 evolution of the higher types of plants. Among the green algae 

 the actual germination of the gametospore is limited to a few 

 hours at trfe most and this is effected in the water, where the 

 conditions are exceptionally uniform. The germination of the 

 gametospore in the case of the liverworts is prolonged over sev- 

 eral weeks, and more important still is the fact that this growth 

 occurs on the land where it is exposed to a wide range of stimuli 

 that cause it to vary in a most remarkable manner. So we must 

 bear in mind the character of this rather*simple growth derived 

 from the gametospore of Ricciocarpus and compare it with the 

 variations that appear in the succeeding forms. 



