Chapter XX. 

 THE SPORE AND THE CELL. 



There is one peculiarity appertaining to matters refer- 

 ring to living things, namely an impossibility to construct 

 a perfect definition. For instance, taking the word spore, 

 we use it freely, and understand fairly well what we mean 

 when we use it, but although in most instances we may 

 accurately define any particular spore, we cannot con- 

 struct a definition to include all spores. 



A spore is a free protoplast enclosed in a cellulose case. 

 Then there are spores which have no case, for instance, the 

 megaspore of a flower. A spore may not be free as in the 

 compound spores of many Fungi. Again, there are many 

 single free protoplasts which are not spores. A spore is 

 a single protoplast which is employed in the function of 

 propagation or reproduction, yet there are other things, 

 such as gemmae, with a similar function, which we do not 

 call spores. Spore production we may trace in the highest 

 to almost the lowest of plant forms. 



A simple form of spore production is that with which 

 we are familiar in the case of ferns and mosses. Sacks 

 are formed full of little spores. When ripe the sack 

 bursts, and the spores are blown about by the wind. In 

 ferns, the spore sacks may be seen like fine brown dust 

 in clusters on the back or margin of the leaf. In mosses 

 the spores are contained in single large cases, commonly 

 referred to as the moss-fruit. In both these instances the 

 spores are all of one size. 



In several distinct instances dam Nature has bethought 

 herself that economy may be effected by producing spores 

 of two sizes; large or megaspores of a passive nature, and 

 small or microspores whose duty it is to fertilise the 

 others. This is the condition we find in many lowly plants, 

 and likewise in Firtrees and Flowering plants. In the 

 latter the microspores are formed in the anthers, and the 

 megaspores in the pistil. 



In the case of an ordinary fern the spores do not grow 

 into young fern plants, but into quite a different form. 

 The spore on germination grows into a small, flat, green, 

 heart-shaped plant, called a prothallium. On the under- 

 surf ace of this the essential organs of reproduction develop ; 

 fertilisation takes place, and a young fern plant is the 



