312 



BOTANY: PRINCIPLES AND PROBLEMS 



Multicellular Sexual Organs. — The sexual organs of the 

 bryophytes have also attained a degree of complexity far above 

 those of the thallophytes. In the latter group, with a few minor 

 exceptions, the structures which produce the eggs and the sperm 

 are modified single cells, the gametes being formed directly out of 

 the cell contents. In the bryophytes, however, the gamete- 

 producing organ has a definite, many-celled wall surrounding the 



Fig. 183. — Multicellular sexual organs of a bryophyte (Ricciocarpus) . A, 

 antheridium. B, archegonium. v, venter, n. neck. A large egg is evident in 

 the venter, but the ventral canal cell and neck-canal cells are largely broken 

 down, following the opening of the neck of the archegonium. See also Figs. 185 

 and 196. 



cell or group of cells which develop into the gametes (Fig. 183). 

 The female sex organ is now known as the archegonium. It is a 

 somewhat flask-shaped structure, the swollen lower portion of 

 which is known as the venter and the elongated upper portion as 

 the neck. The wall is a single cell-layer in thickness. Most of 

 the cavity of the venter is occupied by a large egg-cell, and just 

 above this lies a much smaller ventral canal cell. Filling the neck 

 are a row of narrow neck-canal cells. When wet, the neck opens, 

 the neck-canal cells breakdown, and a sperm enters to fertilize the 

 egg. The male sex organ is still known as the antheridium. In 

 bryophytes it has typically a short stalk and is somewhat elon- 

 gated. Its wall, one cell-layer in thickness, surrounds a mass of 

 small, squarish cells within each of which a motile sperm is 

 developed, provided with two cilia. When wet, the antheridium 



