120 OPPICE OF THE 8EED. 



600. The lbapy natcbe of the cotyledons is often distinctly manifest in their 

 form and structure, as in Convolvulus (455). 



A few plants, as the onion, orange, Coniferaj, occasionally have two or even sev- 

 eral embryos in a seed, while aU the Cryptogamia or flowerless plants have no 

 embryo at all, nor even seeds, but are reproduced from spores, bodies analogous to 

 the pollen grains of flowering plants (469). 



OFFICE OF THE SEED. 



601. Its nature and use. After the embryo has reached its 

 wonted growth in the ripened seed, it becomes suddenly inactive and 

 torpid, yet still alive. In this condition it is, in fact, a living plant, 

 safely packed and sealed up for transportation. This is the distinctive 

 and wonderful nature of the seed. 



602. Longevity of the seed. This suspended vitality of the seed may endure 

 for years, or even, in some species, for ages. The seeds of maize and rye have 

 been known to grow when 30 to 40 years old ; kidney -beans when 100 ; the rasp- 

 berry after 1700 years (Lindley), and kernels of wheat found in a, mummy-case, 

 and therefore 3000 years old, were a few years ago successfully cultivated in Ger- 

 many and England (Sohleiden). Seeds of Mountain Potentilla (P. tridentata) were 

 known to us to germinate at Meriden, N". H,, after a slumber of 60 years. On the 

 other hand the seeds of some species are short-Uved, retaining vitality hardly a 

 year (Coffee, Magnolia). 



603. In order that seeds may long riStain their vitality they 

 must be kept dry. But an even temperature is by no means neces- 

 sary, as they are generally able to resist all the changes of our climate 

 from many degrees below zero to 110° above, provided no moisture 

 is present. 



604. The dispeesion of seeds over wide, and often to distant regions is vi- 

 fected by special agencies, in which the highest intelligence and vrisdom are clearly 

 seen. Some seeds made buoyant by means of the coma, or pappus, already men- 

 tioned, are wafted afar by the winds, beyond rivers, lakes and seas ; as the thistle, 

 dandelion, silkgrass. 



605. Seeds abb also furnished with wings for the same purpose. Others 

 are provided with hooks or barbs, by which they lay hold of men and animals, and 

 are thus, by unwilling agents, scattered far and wide (burr-seed, tick-seed). 



606. Otijeb SEEDS, destitute of all such appendages, are thrown to a distance by 

 the sudden coiling of the elastic carpels (touch-me-not). Tho squirting cucumber 

 becomes distended with water by absorption, and at length, when ripe, bursts an 

 aperture at base and projects the mingled seeds and water with amazing force. 



607. Transportation. Rivers, streams, and ocean currents are all means of 

 transporting seeds from country to country. Thus the cocoa and the ca-skew-nul 

 and the seeds of mahogany have been known to perform long voyac::es without in- 

 jury to their vitality Squirrels laying up their winter stores in the earth, birds 

 migrating from clime to clime, and from island to island, in like manner conspire to 

 effect the same important end. 



