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THE AMERICAN NATURALIST [Vol. XXXVII 



the true roots of the vascular plants allows the development 

 of a root system to keep pace with the growth of the aerial part 

 of the sporophyte. There is thus developed for the first time 

 a plant-body strictly terrestrial in its character, and capable of 

 independent growth. 



The gradual elaboration of the sporophyte is easily traced in 

 the liverworts from the simple capsule of Riccia to the large 

 and almost independent sporophyte of Anthoceros, or in another 

 direction to the elaborate sporophyte of the true mosses. 



Whether or not we agree entirely with Professor Bower's 

 beautifully worked out theory of the sterilization of potential 

 sporogenous tissue, the fact is patent that there has been a 

 gradual elaboration of the originally purely sporogenous and 

 parasitic structure resulting from the zygote, in the direction of 

 an independent plant, with a corresponding subordination of the 

 spore-producing function to the vegetative life of the sporophyte. 

 This culminates among the Bryophytes in such highly specialized 

 types as Polytrichum and other similar mosses. In these there 

 is early developed a foot, which supplies the materials needed 

 for the growth of the long-lived sporophyte. In the more highly 

 organized forms there is present a special strand of water-con- 

 ducting tissue, which may be directly compared to the fibro- 

 vascular bundles of the higher plants. The outer tissues of the 

 long slender seta, also, assume the character of mechanical tis- 

 sues which give it the necessary strength to support the large 

 and complicated capsule, in which only a very small amount of 

 tissue is devoted to spore-formation. 



At an early period the outer tissues of the sporophyte develop 

 chlorophyll, and there may be formed a distinct assimilative 

 organ, the apophysis, provided with green lacunar tissue com- 

 municating with the external atmosphere by means of stomata, 

 entirely similar to those upon the given organs of the vascular 

 plants. The highly specialized sporophyte of the true mosses 

 has not probably given rise to any type of vascular plants, but in 

 the equally developed, but much more generalized sporophyte 

 of Anthoceros, we have a structure that may well represent the 

 characters of the sporophyte from which originated the leafy 

 sporophyte of the ferns. 



