222 



GENERAL BIOLOC.V 



Fig. 119. 



A Moss ( Tetraphia 

 sp.) , showing gemmse ; 

 G., a gemma enlarged. 

 (From C. Stuart Gager's 

 "Fundamentals of Bot- 

 any," by permission of 

 P/Blakiston's Son & Co., 

 Publishers.) 



The so-called true mosses (Fig. 109) have life-histories quite like 

 that of Sphagnum, although there are differences. In true mosses the 

 protonema produces leafy branches (the true moss-plants), but it does 

 not produce a thallus. The leafy branches arise directly from the fila- 

 mentous protonema. True mosses are both monoe- 

 cious and dioecious. There is no pseudopodium 

 (Fig. 118), but the stalk of the sporophyte which 

 is very short in Sphagnum, here elongates to form 

 a seta, often more than an inch in length. 



The true mosses have little breathing pores 

 called stomata at the base of the capsule. Sphagnum 

 has the stomata, but they do not function. Chloro- 

 phyl-bearing cells surround these stomata, so that 

 in the true-mosses there is some food actually man- 

 ufactured by photosynthesis. 



The sporophyte of the true mosses seems to 

 occupy an intermediate position between Sphagnum 

 and the next higher group of plants, the Ferns. 



. . 



There is an increase in sterile tissue as we approach 



r ., . . , 



the terns, and a decrease in fertile tissue in the 

 sporophytes. 



From experiments so far performed it seems 

 that every cell of the moss-plant can, like the tissue-animal Hydra, which 

 we shall soon study, develop a protonema that is, each cell is a poten- 

 tial spore. Each protonema produces buds which become mature plants. 



There are certain species of mosses in which the leafy-shoot, and 

 in others, the protonemata, give rise to a special type of small bodies 

 called gemmae (Fig. 119), ( ), which "become sepa- 



rated from the parent plant and give rise to new plants. 



A comparison of Sphagnum and a fern (to be studied next) is of 

 value here. 



The commonly known "fern-plant" is a sporophyte while the Sphag- 

 num-plant is a gametophyte. 



The fern sporophyte is dependent on the gametophyte for nutrition, 

 at first, then the sporophyte becomes entirely independent, while the 

 simple gametophyte perishes. 



The Sphagnum sporophyte is the simpler plant and it is this sporo- 

 phyte which must depend upon the gametophyte for nutrition through- 

 out its entire life. 



Reproduction is quite alike in Fern and Sphagnum. Each produces 

 haploid gametes of two sexes, which then unite in fertilization, the zygote 

 being diploid. It is the zygote which produces the spore-bearing phase. 

 The spores, which are in turn haploid due to a reduction having taken 

 place, then give rise to the haploid gametophytes, so that we may sum 

 tip the life-cycle in both Fern and Sphagnum by saying: Gametophyte 



