230 



MORPHOLOGY. 



i^4 



surface, while the dcKcate, 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 sec the relation 



of the gametophore to the thaUus of 

 marchantia take portions of the 

 thallus bearing the female recepta- 

 cle. On the under side note that 

 the prominent midrib continues be- 

 yond tlie 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 apc.x of this are organized sev- 

 eral radial growing points \\'hich 

 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, 

 ai)pears to arise from the upper 

 surface, as in fig. 261. This is 

 because the thin lateral expansions 

 Marchantia pulymorpha, showing origin of the thallus project forward and 

 of gametophore. " _^^,^j.,^p j^ advance of the stalk. It 



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

 real origin of the gametophore. Hut in i|uite old plants these expanded 

 portions are farther apart and show cli-arly that the stalk arises froiri the 

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



