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comes divided after a short time, and becomes an aggregation 

 of little cells, which take the shape, when expanded, of a minute 

 patch, like a tiny leaf laid flat on the ground. This leafy scale 

 is mostly irregular in shape, and usually somewhat round or 

 heart-shaped, green in colour, and named a prothallus, from 

 two Greek words pro before, and thallus a young shoot. 

 Under the prothallus, which attaches itself to the earth by fine 

 rootlets, other cells begin tO' be produced. These are of two 

 kinds, and produce respectively the sperm cell and the egg cell, 

 and with these commences a new life history. The germ must 

 be fertilised before it can commence the process of develop- 

 ment. The sperm cell breaks up into^ minute active, thread- 

 like bodies, called spermatozoids. When it is ripe the ovum, or 

 egg-cell, which is at the bottom of a flask-shaped mass of cells 

 called the Archegonium, is put into communication with the 

 exterior by the breaking down of the cells into mucilage, and 

 this mucilage has the power of attracting the spermatozoids. 

 The latter are set free by the action of water on the organ, the 

 antheridium, in which they are contained, and they swim about 

 in a drop of the water on the prothallus until they reach the 

 egg-cell, with which one unites. This process is called 

 "fertilization," and the resulting cell by subdivision gives rise to 

 a new fern plant. Thus a spore gives rise, not to a fern plant, 

 but to a prothallus, which, in its turn, produces cells which 

 gives rise to a fern plant. This is what is known as "alterna- 

 tion of generations." The young fern plant grows up through 

 the prothallus, which soon rots and disappears. Steadily the 

 process of development continues, until a tiny fern is produced, 

 whose form and habit begin to assume a likeness to the parent 

 plant. In most ferns, the process of development is very slow, 

 several years being occupied before it is completed. 



To recapitulate: — On germination, each spore gives rise to a 

 prothallus, and leads quite an independent existence. The 

 prothallus is a flat, green, heart-shaped body, sometimes as 

 much as half an inch in diameter, attached to the soil by the 

 root hairs which arise from its under surface. Prothalli may 

 be found in abundance covering the damp ground where ferns 



