230 



MORPHOLOG y. 



surface, while the delicate, pendulous fringes afford them pro- 

 tection from drying. An archegonium we see is not essentially 

 different in marchantia from what it is in riccia, and it will be 

 interesting to learn whether the sporogonium is essentially dif- 

 ferent from what we find in riccia. 



487. Homology of the gametophore of marchantia. To see the relation 

 of the gametophore to the thallus of 

 marchantia take portions of the 

 thallus bearing the female recepta- 

 cle. On the under side note that 

 the prominent midrib continues be- 

 yond the thin lateral expansions and 

 arches upward in the sinus or notch 

 at the end, or at the side where the 

 branch of the thallus has continued 

 to grow beyond. The stalk of the 

 gametophore is then a continuation 

 of the midrib of the thallus. On 

 the apex of this are organized sev- 

 eral radial growing points which 

 develop the digitate or ray-like 

 receptacle. The gametophore is 

 thus a specialized branch of the 

 thallus. When young, or in many 

 cases when nearly or quite mature, 

 the gametophore, as one looks at 

 the upper surface of the thallus, 

 appears to arise from the upper 

 surface, as in fig. 261. This is 

 because the thin lateral expansions 



Marchantia polymorpha, showing origin of the thallus project forward and 

 of gametophore. overlap in advance of the stalk. It 



is sometimes necessary to tear these overlapping edges apart to see the 

 real origin of the gametophore. But in quite old plants these expanded 

 portions are farther apart and show clearly that the stalk arises from the 

 midrib below and arches upward in the sinus, as in fig. 262. 



Fig. 262. 



