







Durand : Marchantia polymorpha 329 



the first place the collar at the base of the archegonium, which is 

 inconspicuous before fertilization {figs. 63, 69), by transverse 

 division of its cells grows rapidly outward until it forms a tubular 

 sheath, the pseudoperianth, surrounding the venter, and ultimately 

 projecting far beyond it. This is always a single layer in thick- 

 ness {Jigs, 70, 76, 88, 92, 94). In the second place, periclinal 

 division begins in the wall of the venter, and continues until two 

 or three layers of cells are formed at the sides of and above the 

 embryo. The tissue thus formed is the calyptra, which serves as 

 a protective covering for the growing embryo {figs. 70, 71, 70, 81, 

 82, 88-90, 92, 94-98). The contents of its cells soon become 

 richer so that it is stained more deeply. 



The third series of changes is in the base of the venter and in 

 the cells immediately beneath it, from which the pseudoperianth 

 arises {fig. 70). Division takes place in all directions so that the 

 base, originally narrow and rarely more than three cells across, 

 becomes broad and massive {figs. 70, 76, 88, 92, 94). The cells 

 thus formed from the base of the archegonium are generally 

 smaller than those of the adjacent gametophore {fig. 94), and soon 

 become rich in protoplasmic content and stain deeply. 



The embryo and surrounding tissues now enlarge rapidly and 

 the contents of all the cells increase in staining capacity {fig- 94)> 

 This is especially noticeable in the tissue beneath the embryo, 

 derived from the base of the archegonium. The embryo itself 

 becomes nearly spherical {figs. 94-97), and then broader than 

 lon g {figs. 98, 99). The- first indication of its differentiation into 

 parts is a change in the staining capacity of the cells. Those in 

 the distal half become richer in protoplasmic content, and form the 

 capsule, while those of the proximal half stain with less avidity, 



' give rise to the stalk and foot {figs. 95, 9 6 \ An ins P ection 



and 



/. 



_, ,„.. ... j, S ..,s. yj 



sular halves are separated by the first transverse division-wall, and 

 this is usually the case. That it is not always true, however, is 

 shown in figure 96. In this embryo the original walls were 



A 



In such cases the first 



division-wall does not separate the embryo into the stalk and cap- 

 sular halves, but this differentiation is determined by other influ- 

 ences. In general it is true that, whatever be the direction of the 



