THE YOUNG NATUEALIST. 



63 



tained in one case. It has been calculated, 

 that a single frond of the male shield fern 

 (Lastrea felix-mas), bore upwards of ten 

 thousand collections of spore cases, from 

 which no fewer than one hundred millions 

 of ripe spores would be produced ; thus if 

 an ordinary fern plant produced ten fronds, 

 the total number produced by the whole 

 plant would be little short of one thousand 

 millions. Each of these minute spores 

 consists of a little case containing a speck of 

 living matter called protoplasm. No struc- 

 ture is distinguishable in it. Yet it is 

 adapted and intended by nature, to repro- 

 duce through developement the form of the 

 parent organism. 



When the season arrives for the dispersion 

 of the spores, the indusium shrivels up and 

 lays bare the spore cases, the rings of the 

 spore cases, in turn, suddenly burst, and 

 the spores are scattered in all directions, 

 and as they are so very small, the least waft 

 of wind may carry them a considerable 

 distance. 



The time which elapses between the 

 dispersion of the spores, and their germina- 

 tion, depends greatly upon the conditions 

 v/hich surround them. If the soil be 

 favourable, they may commence their new 

 existence at once. 



As we shall presently see, the result of the 

 germination of fern spores, differs very much 

 from that of ordinary flowering plants, such 

 as the pea for example, for when a seed of 

 the pea is planted, we naturally expect a pea 

 to grow up directly therefrom. In this as 

 in other flowering plants we are not dis- 

 appointed. But the fern spore behaves very 

 differently. At first it expands in the form 

 of a simple oblong cell, from which other 

 cells are successively produced, and 

 ultimately forming, instead of a fern, a 

 curious leaf like body, known as the pro- 

 thallus, which lies almost flat to the ground, 

 and by means of fine rootlets, attaches 

 itself to the surface, and likewise absorbs 



nourishment. When arrived at its full size it 

 is from i to ^ inch in diameter, in some 

 species it is heart shaped, and in others 

 somewhat rounded. In the progress of 

 growth peculiar cells are formed on its 

 under surface, which are of the highest 

 importance in fern history. They are of 

 two kinds, one called anthef idia, and the 

 other arcTiegonm. These cells perform 

 precisely the same functions as the stamen 

 and pistil of flowering plants, and if ferns 

 can ever be said to produce flowers it is at 

 this time. 



If we carefully examine the prothallus, 

 near the origin of the root fibres, we shall 

 find a considerable number of these anther- 

 idial cells, and we shall also notice that 

 they contain peculiar spiral threads technic- 

 ally termed spermatozoids. 



The archegonia are found on a different 

 part of the prothallus, and are fewer in 

 number. In these are contained the germ 

 cells. When we notice the process by 

 which these germ cells are fertilized, we 

 are at once struck with its great resemblance 

 to that of ordinary flowering plants. 



When antheridia have reached maturity, 

 the cells burst, and liberate the curious 

 spiral threads, which as soon as they are 

 free, move about the under surface of the 

 prothallus, as though endowed with animal 

 life ; eventually they come in contact with 

 the archegonia, reach the germ cells, and 

 thus fertilize them. The germ cells are now 

 changed, and a bud is formed, and ultimately 

 a young fern plant is gradually developed. 

 For some time the prothallus remains 

 attached to the young fern, and supplies it 

 with nourishment, but when its functions 

 as a nurse are discharged, it decays away, 

 and the fern grows more and more in the 

 likeness of the adult, and in time produces 

 the spore cases and spores, which repeat 

 once again this curious history, which is 

 known to biologists, as the alternation of 

 generations. 



