THE ARCHEGONIAT^E 195 



In the lower Archegoniates, however, although they are more or 

 less dependent upon an ample supply of moisture, the plant 

 develops various devices for protecting it against the loss of water. 

 Koots of some kind are always present, which penetrate into the 

 substratum and renew the supply lost by evaporation, which is, 

 moreover, checked by the development of an impervious cuticle upon 

 the cells exposed to the air. These devices, which are only imper- 

 fectly developed in the lower forms, become extraordinarily perfect 

 in many of the higher types of land-plants. The conditions being 

 so much more variable on land than in the water, the terrestrial 

 plants show a correspondingly greater diversity of structure than is 

 ever found in aquatic forms. 



None of the Archegoniates possess motile cells corresponding to 

 the non-sexual zoospores of the Algae, but all of them give rise 

 to motile spermatozoids, which require water in order to reach 

 the archegonium which contains the egg; and this reversion to the 

 aquatic condition as a preliminary to fertilization indicates the 

 aquatic origin of all these forms. 



The formation of res ting-spores occurs in all of the Archegoniates; 

 but instead of the fertilized egg developing at once into a resting- 

 spore, as it does in most Green Algae, the egg develops into a multi- 

 cellular plant, the Sporophyte, which then gives rise, non-sexually, 

 to a large number of resting-spores. One fertilization may therefore 

 result in an enormously larger number of spores than is the case 

 among the Green Algae. The development of the carpospores of 

 the Red Algae offers an analogy to this, although the method of 

 spore-formation is totally different. 



In a few Liverworts (e.g. Elcciocarpus, Fig. 163) the plant usually 

 lives as an aquatic, but it may assume a terrestrial form by settling 

 on the mud after the subsidence of the water, and there grow even 

 more vigorously than it did when floating in the water. Sometimes 

 the plant only develops its reproductive parts when it thus assumes 

 the terrestrial form. The behavior of Ricciocarpus probably illus- 

 trates the way in which the terrestrial Archegoniates first began to 

 take possession of the land. 



With the Seed-plants the Archegoniates are sometimes put in 

 a single great division, the Embryophytes, so called because the 

 fertilized egg develops into a multicellular embryo before the spores 

 are formed. All of the Archegoniates agree closely in the character 

 of their reproductive parts, and there is little question that the 

 subkingdom is a very natural one. 



Alternation of Generations. All Archegoniates show two phases 

 of development. The spore, on germination, produces a plant, the 

 gametophyte, upon which are borne the sexual reproductive organs, 

 archegonia and antheridia. From the egg, within the archegonium, 



