APPENDIX. 465 



From these observations it is clear that the ripe spore-cases 

 burst open in dry weather and scatter the spores, which are 

 very light and easily carried about by the wind. The indu- 

 sium protects the young growing spore-cases, and becomes 

 shrivelled up and withered when they are ripe. The spore- 

 cases are also protected by being produced on the lower side 

 of the leaf. 



The spores are very small, and are one-celled bodies, with a 

 thick outer coat and a thin inner coat. The spores of ferns 

 and other flowerless plants are sometimes called seeds ; but 

 it is clear that a spore is very different from, and almost 

 infinitely simpler than, a seed. A seed contains a young 

 plant, with cotyledons, root, and shoot, and often a store of 

 food outside of the embryo as well ; a spore is a single cell. 



What becomes of the spores when they are set free? 

 Instead of searching the neighbourhood of the plant itself, 

 sow the spores and keep them under observation indoors. 

 Dry a leaf on a sheet of paper, which will soon be covered 

 with the dust-like brown spores, and sow them on soil or bits 

 of brick or tile. The soil (lumps of peat or leaf-mould are 

 perhaps best), or the bits of brick or tile, should be either 

 baked in a hot oven for some hours, or else steeped in boiling 

 water, to destroy the germs of fungi that are apt to damage 

 or destroy the germinating spores. Shallow dishes should be 

 used, with some water in them, for the spores should not be 

 watered from above; this would wash them away. The 

 cultures should be shielded from direct sunlight, that the 

 spores may germinate more rapidly. 



On germination, for which the same things are essential as 

 in the case of a seed oxygen, water, and warmth the outei 

 coat of the spore breaks open, and the contents escape, 

 covered by the thin inner coat, as a green thread, from which 

 a colourless thread (root-hair, or rhizoid) is given off into the 

 soil. The green thread grows along the surface and soon its 

 end broadens out (Fig. 6). Eventually a heart-shaped green 

 plate, the prothallus, is formed ; it is about one-third of an 

 inch across. 



The prothallus consists of angular cells, containing abundant 

 chloroplasts. Towards the margins it is only one cell in thick- 

 ness, but the central part, or cushion, consists of several layers 

 of cells. Long root-hairs grow from the lower surface. The 

 s. B. 30 



