MOSSES A:s^D LIVEEWOKTS (BRYOPHYTES) 269 



of cells. These older mature gemmae are flat, and have two 

 marginal notches, between which there is a marginal scar 

 showing where the gemma was attached to the stalk upon 

 which it grew. The gemmae may grow directly into new Mar- 

 cJiantia plants, the notches being the points at A^hicli growth 

 begins. ^Yhichever side is adjacent to the earth develops 

 rhizoids and becomes the ventral side, while the other becomes 

 the dorsal side. One can determine wliich side of a gemma 

 shall develop rhizoids or air chambers by the side of the 



Fig. 224. Marchantia antheridial head, antheridia, and sperms 



At the left is a section of an antheridial head, showing several antheridia (a) em- 

 bedded near the surface. At the right is shown one antheridium in detail, and 

 at its side are two sperms (s) somewhat enlarged. After Sachs 



gemma which is placed next to the soil. Even after growth has 

 begun, if the gemmae are overturned, the development from 

 and within the surface tissues will change to that which is 

 characteristic of lower and upper surfaces respectivelv. Forma- 

 tion of gemmae provides Marclmntia with a read}' and abun- 

 dant method of vegetative reproduction. 



251. iWarc^anfta; sexual reproduction. From the midrib region 

 of the flat Marclmntia body there sometimes grow upright stalks 

 (Fig. 223). The tips of these stalks bear heads of two distinct 

 kinds. One head (antheridial) is flat above and has a slightly 

 indented or wrinkled margin. The other (archegonial) is more 

 drooping and has finger-like rays extending from its main body. 



