THE MARCHANTIAS 409 



tures are further differentiations of the plant body, that are not 

 always present, occurring only during periods of reproduction. 

 The erect umbrella-shaped structures, which are upgrowths of 

 the midrib of the thallus, bear the sex organs and are called 

 gametophores, while the cup-shaped structures have to do with a 

 vegetative method of reproduction which will be discussed later. 



Since the plant lives spread out on a moist substratum, much 

 of the plant body is in direct contact with moisture and can 

 absorb water and minerals directly. The rhizoids are not roots 

 and are of very little service in supplying water and mineral salts. 

 It is probable that they do nothing more than hold the plant 

 body to the substratum. The filaments of cells in the air cham- 

 bers on the upper surface are well provided with chloroplasts and 

 carry on active photosynthesis which supplies the plant with 

 carbohydrates. Many of the other cells in the upper region of 

 the plant body have some chloroplasts and no doubt assist some 

 in providing food. 



In addition to the sexual method of reproduction, there are 

 two ways of propagating vegetatively or asexually. As the 

 branches of the thalli develop and push ahead, the older regions 

 die away and soon the branches become isolated and form sepa- 

 rate plants. This is known as a vegetative or asexual method of 

 reproduction because no spores or sex cells are involved. An- 

 other vegetative method occurs in connection with the cups 

 which have been pointed out on the surface of the thalli. In 

 these cups are produced small plates of cells, called gemmae, 

 which, when splashed out by rain and suitably located on a 

 substratum, grow directly into new plants. These vegetative 

 methods remind one of the propagation of Strawberries by run- 

 ners, or of Geraniums by cuttings. 



The sex organs are produced upon the umbrella-like tops or 

 receptacles of the gametophores. On the under surface of the 

 much lobed receptacles of the gametophores of the female plants 

 (A, Fig. 363) occur the female sex organs called archegonia. 

 When a thin section is made through a female receptacle and 

 examined under the microscope, the archegonia are seen pro- 

 jecting from the under surface as shown at A in Figure 365. 

 Each archegonium consists of many cells so arranged as to form 

 a long hollow neck and an enlarged hollow base called venter, in 

 which the large egg is located. It is obvious that an archegonium 



