Plant World Continued 



223 



A 

 sp.), 



G., a 

 (From 



Moss (Tetraphis 



showing gemmae; 



gemma enlarged. 



C. Stuart Gager's 



"Fundamentals of Bot- 

 any," by permission of 

 P. Blakiston's Son & Co., 

 Publishers.) 



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 

 the ferns, 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 up the life-cycle in both Fern and Sphagnum by saying: Gameto- 

 phyte alternates with sporophyte, fertilization with reduction, gametes 

 with spores, haploid cells with diploid. 



