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A TEXTBOOK OF THEORETICAL BOTANY 



is produced within the archegonium, which develops into the spore-producing 

 capsule, or sporogonium. This sporogonium, as we have seen, lives per- 

 manently upon the female gametophyte, and we may conclude from the 

 fact that the foot is thrust down into the apex of the receptacle that 

 the sporogonium obtains a considerable amount of food material from the 

 gametophyte, and that it by no means relies entirely upon the chlorophyll 

 cells which are developed in the capsule. 



The living cells of the sporogonium have the power of producing 

 secondary protonemal outgrowths, especially if they are in contact with 

 damp soil. This protonema is, of course, diploid and the gametophytes 

 which develop from it are likewise diploid. In such cases fertilization will 

 produce tetraploid sporophytes. By the repetition of this procedure 

 experimentally a 32-ploid plant has been arrived at, but this seems to be 

 the limit, as the plant was sterile. 



We can illustrate the life history of Mniiim by Fig. 416. 



Polytrichum commune 



Our second example, Polytrichum commune, is one of the most highly 

 developed types of Moss. It is found commonly in this country growing on 



Fig. 417. — Polytrichum cotnmtine. Plant with ripe 

 sporogonia. Slightly reduced. 



moors and bogs and sometimes in woodlands, always preferring wet soils. 

 In size it varies very considerably according to the environment, and some- 

 times when growing among long grass on a damp, peaty marsh, it may reach 

 30 cm. or more in length (Fig. 417). 



Fhe anatomy both of the leaf and stem shows considerable complexity 



