CHAPTER XIV. THE SPERM APHYTA. 363 



others, as the giant Sequoia, attain the lofty height of more than 

 four hundred and twenty feet. Some pass through the complete 

 round of their life-history in a few days, while others outlive 

 many generations of men ; some have a soft, flabby structure, 

 and are easily destroyed, while others are composed chiefly of 

 hard and enduring tissues ; some make their homes in the water, 

 others in marshy places, others on dry ground, while still others 

 prefer the arid wastes of the desert : some are parasitic or sapro- 

 phytic, but the great majority are chlorophyll-bearing; some 

 like the shade, others prefer the open sunshine ; some nourish 

 only on the borders of eternal snows, while others cannot thrive 

 except in the perpetual warmth of the tropics ; and there are 

 indeed few corners of the earth so inhospitable as not to afford 

 some of them a congenial abiding-place. 



While it is probably true that, merely in the number of indi- 

 viduals, they are surpassed by some of the lower classes of Thal- 

 lophyta, in the number of species they probably exceed all the 

 other Series of plants put together. 



The term Spermaphytaox Seed-plants, is appropriately applied 

 to the members of the Series, because their most distinctive char- 

 acteristic is the production of seeds. These, as we have alreadv 

 seen, are entirely different bodies from spores, being much more 

 complex in their structure, containing within their seed-coats an 

 embryo or plantlet which is usually so far developed as to possess 

 the rudiments of stem, root and leaves. They often also contain 

 an endosperm or perisperm, whose service is to nourish the 

 growing embryo. 



Since none of the lower plants produce seeds, there would 

 seem, at first thought, to be a sharp line of separation between 

 Seed-plants and all others, but such is not really the case. The 

 process of seed-production is now known to be closely related 

 to the sexual processes in the Pteridophyta, and the progress from 

 the lowest forms of the latter group to the highest forms of Seed- 

 plants, is one of easy gradations. 



In both groups the reproductive organs are, with a few excep- 

 tions, borne upon the leaves ; in the Seed-plants, however, par- 

 ticularly in the higher forms, these leaves, and often also others 

 indirectly concerned in the reproductive process, are much more 

 strongly modified and form a more or less conspicuous group, 



