THE VARIOUS FORMS OF PLANTS 153 



If we were to plant the spores of the moss in damp sand, taking care to 

 keep the sand moist and warm, we might get tin-in to grow. Tin- 

 spore germinates into a threadlike structure, very tiny, and not at all 

 like the adult moss plant. This thread is called a i>rt>ttnn ma. 



Adult Moss Plants. The protonenia soon develops rhixnids ; tiny 

 buds appear which in time form the adult moss plant. These adult plants 

 may grow only leaves, and become what are known as steiile plants; or 

 they may develop into a plant that bears at the summit the little rosette 

 of leaves previously referred to. Within the rosette lie a number of tiny 

 organs which hold large numbers of sperm cells. Other moss plants not 

 so tall as the sperm-producing plants bear at the summit of the stem a 

 tuft of leaves which hide a number of small Husk-shaped structures, each 

 of which contains a single egg cell. These plant* farm tin- sexual genera- 

 tion of the mo**. Tin'* *t nje of the plant i* called the </a tin /<>/>lti/lc, because 

 it i>railueex the gametes or sexual << //.-;, eggs and sperms. After a sperm 

 cell has been transferred (usually by means of a drop of dew) to the egg 

 cell, a fusion of the two cells takes pl.u-e. This, we remember, is the pro- 

 cess of f< rtil/:ati<i. In the mosses the t'ertili/.at ion of the egg cell results 

 in the growth of that part of the plant which forms and bears the asexual 

 spores. 



Alternation of Generations. In the mosses we have what is known 

 as an alternation of generation*. The leafy moss, beaiing among its leaves 

 the organs producing sperms and eggs, nntluriilia and archegonia, gives 

 pl-ice to a stalk and capsule bearing the i>*esmil spores. This spore-bear- 

 ing portion of the plant does not appear until after fertili/ation ; then it 

 grows directly out of that part of the plant which produces the egg cell. 

 In fact, if we make a microscopic examination of the egg-producing struc- 

 ture (the a re In >/<>nium) directly after fertili/ation. we find that the sporo- 

 phyte is a direct outgrowth from the fertilized egg cell. Thus the sexual 

 stage alternates with the asexual stage in the life of the plant. 



Sporophyte a Parasite. One interesting fact comes out i-i connection 

 with this growth of the sporophyte. It has no green lea\vs and must 

 therefore obtain all its nourishment from the leafy moss plant, or game- 

 tophyte. The spore-bearing part of the plant is thus actually a parasite 

 upon the gametophyte. 



Ferns and their Allies 



The Ferns and their Allies. The fern plants include the true ferns, 

 the horsetails or scouring rushes, and the club mosses. The true ferns 

 are moisture-loving and shade-loving plants ; they play an important part 

 in the vegetation of the tropical forests. Many forms are found in the 

 temperate regions ; we even have some common ferns that remain green 

 all winter. Fossil ferns have been found in Greenland, thus showing that 

 at one time the climate at the north was milder than it now is. 



