LIVERWORTS: RICCIA. 



223 



Fig. 252- 

 Thallus uf Riccia cn'stallina. 



nearly to the central point. They are not real slits, however, for 

 they were formed there as the jjjaiit gre\v. Each one of these 

 V-shaped portions of the thal- 

 lus is a lobe, and they were 

 formed in theyouiigrondition 

 of tlie plant hy a branching 

 in a forked manner. Since 

 growth took place in all direc- 

 tions radially tlie ]jlant be- 

 came circular in form. These 

 large lobes we can see are 

 forked once or twice again, 

 as shown by the seeming 

 shorter slits in the margin. 



476. Sexual organs. — In 

 order to study the sexual organs we must make thin sections 

 through one of these lobes lengthwise and perpendicular to the 

 thallus surface. These sections are mounted for examination 

 with the microscope. 



477. Archegonia. — We are apt to find the organs in various stages of de- 

 velopment, but we will select one of the flask-shaped structures shown in tig. 

 253 for stud}'. Tills flask-sliaped l_Hjd_)' we see is entirely sunk in the tissue 

 of tlie thallus. This structure is the female organ, and is what we term in 

 these plants the arcAegonitim. It is more complicated in structure than the 

 oogonium. The lower portion is enlarged and bellied out, and is the venter 

 of the archegonium, while the narrow portion is the neck. We here see it in 

 section. The wall is one cell la\'er in tliickness. In the neck is a canal, 

 and in the base of the venter wt see a large rounded cell with a distinct 

 and large nucleus. This cell is the i^^'g cell. 



478. Antheridia. — The antheridia are also borne in cavities sunk in the 

 tissue of the thallus. There is here no illustration of the antheridium of this 

 riccia, but fig. 259 represents an antheridium of another liverwort, and there 

 is not a great difference between the two kinds. Each one of those little rect- 

 angular sperm mother cells in the antheridium changes into a swiftly moving 

 body like a little club with two long lashes attached to the smaller end By 

 the violent lashing of these organs the spermatozoid is moved through the water, 

 or moisture which is on the surface of the thallus. It moves through the canal 

 of the archegonium neck and into the egg, where it fuses with the nucleus of 

 the egg, and thus fertilization is effected. 



