1 42 THE PLANT CELL. 



Germination of a spore consists in the swelling and ultimate 

 rupture of its outer wall, and protrusion of the inner thin-walled 

 cell in the form of a tubular growth. This protrusion is soon 

 divided into two cells by tlie formation of a wall, and subse- 

 quently a large number of cells are formed, the whole mass 

 being the rudimentary gametophyte or prothallus (sexual genera- 

 tion). Chloroplasts soon appear in the cells of this structure, 

 which ultimately takes on the form of a small cordate mass, 

 notched or bilobed at the broader end. It is flat, and only a 

 few cells tliick. The upper surface is smooth, and on the under 

 surface are found towards the apex — (i) A number of rhizoids, 

 which serve both as organs of attachment and absorption. 

 Each rhizoid is somewhat like a long root-hair, onlj^ thicker, 

 (ii) The sexual organs. These are the antheridia and oogonia; 

 their origin and subsequent changes will be described separately. 



b. The Sexual Organs, with their Origin, and the Essential 

 Cells. — As mentioned above, the male organ (antheridium) and 

 the female organ (oogonium) arise in the under surface of the 

 gametophyte, or prothallus. Each antheridium is, when mature, 

 a rounded structure, which is formed from a single cell of the 

 under surface of the prothallus, this cell undergoing certain 

 divisions which result in the formation of an external layer of 

 cells, enclosing a mass of cells known as the mother-cells of the 

 antherozooids. These latter form the essential male, or fer- 

 tilising elements (see Fig. 107, 4, 5). The maturation of an 

 antherozooid consists in the occurrence of changes in the nucleus 

 and cytoplasm of the mother-cell. During this process the 

 nucleus (chielly the chromatin portion) becomes elongated and 

 specially curved, one end being thicker than the other, and over 

 the whole a thin film of cytoplasm is present. At the thin end, 

 or tail, are two or three long vibratile cilia, formed, in all pro- 

 bability of ectoplasm, or kinoplasm; whilst at the thicker end, 

 or head, is a vesicle, which is cytoplasmic in nature, and con- 

 tains a few vacuoles and granules of food-material (probably 

 starch). 



Each antherozooid is, by virtue of the possession of vibratile 

 cilia, a motile cell, and swims about in the droplets of moisture 

 on the under surface of the prothallus. Its further history is 

 perhaps better postponed until after the study of the oogonia. 



The oogonia are also formed on the under surface of the 



