GROWTH OF PLANTS PROM THE SEED. 25 



corn, or it may be hardly distinguishable from the secon- 

 dary roots, as is the case with wheat. 



Seedlings of pines and their allies (gymnosperms), aside 

 from the fact that many species have more than two coty- 

 ledons, can hardly be said to possess characters seedlings of 

 specially distinctive of their class. In many gymnosperms. 

 cases the testa is carried up on the tips of the cotyledons, 

 and afterwards thrown off by their bulging outwards. In 

 some species the cotyledons remain under ground. 



Cotyledons, as a rule, perform functions widely different 

 from those of ordinary green leaves, and accordingly pre- 

 sent striking modifications of form and structure. « ^ , ^ 

 While in some cases they unfold and deport and their mod- 

 themselves as foliage leaves, in others, as for "°^'""^^' , 

 example the pea and acorn, they have lost nearly all 

 resemblance to leaves, and serve merely as storehouses of 

 reserve materials ; while in still other cases, as in the grain 

 of corn or wheat, the cotyledon becomes largely an organ 

 of absorption. Interesting transitional forms are seen in 

 the common bean and other plants in which the cotyle- 

 dons rise above the surface and turn green, but soon dry 

 up after their reserve materials are exhausted. The 

 embryos of some dicotyledonous plants produce but one 

 cotyledon, the other being rudimentary. A curious in- 

 stance is that of the orange, in the seed of which several 

 embryos are formed with cotyledons varying greatly in 

 size. In various species of cacti both cotyledons are rudi- 

 mentary, being represented by minute bodies only a milli- 

 meter or two in diameter. In the latter case the radicle is 

 thickened and serves as a storehouse, the cotyledons be- 

 come superfluous, and are finally reduced to insignificant 

 appendages, an illustration " of the principle of compensa- 

 tion or balancement of growth, or, as Goethe expresses it. 



