468 



HUTCHINSON'S POPULAR BOTANY 



absorbs the tissue of the nucellus. In plants of the "Water-lily and Pepper 

 orders (Nymphseacese and Piperacese) and a few others, a portion of the 

 nucellus remains, and forms what is known as perisperm. When both the 

 endosperm and perisperm are completely used up by the embryo in the course 

 of its development, the ripe seed consists simply of a seed-coat (formed from 

 the integuments of the ovule) and the embryo, and is described as ex- 

 albuminous. In cases where the ripe seed contains endosperm as well 

 as the embryo, it is called an albuminous seed. As we have already 

 dealt with the subject in Chapter VI, we need not retrace the ground here. 



From what has been said, however, the distinction between a fruit and 

 a seed must be at once evident. The former is a ripened and developed 



ovary ; the latter, an impregnated 

 and matured ovule. The fruit, in 

 fact, contains the seed or seeds, 

 just as the ovary contains the 

 ovule or ovules. In the Gymno- 

 sperms, which have naked ovules, 

 the seeds are of necessity naked 

 also ; hence they are not true 

 fruits. True fruits are, indeed, 

 confined to the Monocotyledons 

 and Dicotyledons. 



In dealing with the diversi- 

 ties of form and external struc- 

 ture of fruits and seeds, it is 

 interesting to consider them in 

 the light of Adaptation. By this 

 means the inquiry is immensely 

 simplified ; for it is evident that 

 those diversities are mainly di- 

 rected to one end the dispersion 

 of the seed. The seed, in fact, 

 must be adapted to travel. 

 Now seeds and fruits were great travellers centuries before Vasco da 

 (lama and Columbus were heard of, and had crossed seas and continents, 

 and planted colonies all over the world long before the earliest caravan set 

 out from Bactria, or the first Phoenician merchantmen spread sail on the blue 

 waters of the Mediterranean. The necessity for becoming travellers was 

 imposed upon the vegetable community from the outset. Had those old- 

 world fruits just fallen from their parents' arms, so to speak, and lain where 

 they dropped, the consequences must have been disastrous. In a few years 

 vegetation would have been almost choked ; the strongest plants would have 

 killed out the weaker, whole families of plants would have thus become ex- 

 tinct, and the distribution of the remainder would have been much retarded. 



FIG. 574. WOOD-SORREL (Oxalis) 



EXPELLING ITS SEEDS. 



