STRUCTURE OF FERNS. 



9 



cerned, form two valves (fig. 5). The interior of the spore- 

 cases are filled, when mature, with the minute brown dust- 

 like spores or seeds. 



The development of ferns from spores is very curious, 

 and difi'ers considerably from the ordinary development 

 of plants from seeds. 



It is just because this process difi'ers so much from our 

 ordinary experience of growth in plants, that it will be 

 difiicult to explain satisfactorily, without the use of tech- 

 nicalities, how it takes place. Within a reasonable time 

 after sowing the seeds, or spores, growth commences. 

 Usually one or two seed-leaves are produced in common 

 plants, such as mustard-seed sown for small salad. In 

 the latter case the seed-leaves are very difi'erent in form 



Fig. 3. Fig. 4. Fig. 5. 



from the leaves which are produced afterwards by the 

 same plant. But in ferns not only is the form difi'erent, 

 but the function is also difierent. When the fern spores 

 germinate, a kind of filmy green membrane is produced, 

 which cannot be called a leaf: it lies flat upon the soil, 

 adhering by means of delicate rootlets proceeding from 

 its under surface, and when mature is lobed or almost 

 heart-shaped. This delicate "false leaf" is technically 

 named a protliallus. It is useless our attempting to give 

 to this first leaf in ferns a name which is capable of being 

 popularly understood, because the thing itself has no re- 

 presentative in ordinary experience. The use is not that 

 of an ordinary leaf, the mode of growth and structure is 

 not that of a leaf, and to call it " a leaf" would only con- 



