IV.] SUMMARY. 43 



may be well to review here some general characters afforded 

 both by the reproductive and nutritive organs, which are 

 common to all those we have already done, and which are 

 more or less markedly in contrast with the characters pre- 

 sented by the corresponding organs of the plants yet to 

 be examined. 



In nearly all the plants examined you find the leaves with 

 a distinct blade and petiole ; and, if you hold the blade of 

 any of them up to the light, you may notice that the small 

 veins which ramify through it are netted irregularly. In the 

 flowers, you have observed that the parts of the calyx (sepals) 

 and of-the corolla (petals), whether free, coherent, or adherent, 

 are either in fours or jives ; that is, four or five to a whorl. 



12. Now the characters of (i) leaves more or less dis- 

 tinctly narrowed at the base into a petiole ; of (2) irregularly 

 net-veined leaves ; and (3) the arrangement of the parts of 

 the flower in fours or fives (which three characters we have 

 found to apply more or less to all the specimens which we 

 have examined hitherto), are supported by other characters 

 afforded by the seeds and mode of growth of the wood, 

 which it is important you should correctly understand. 



13. If we put a few peas upon moist earth in a flower-pot 

 and cover them with a bell-glass, the first stage of growth, 

 termed genninatiofi, of the young pea-plant may be con- 

 veniently observed. The essentials to germination are found 

 by experience to be a certain amount of moisture, warmth, 

 and air. If sufficiently warm (and the amount of warmth 

 required to commence with varies in the seeds of different 

 plants), moisture is absorbed by the seed, which causes it 

 to swell up so as to burst the seed-skin. Oxygen also is 

 absorbed from the air, and certain chemical changes, accom- 

 panied with the liberation of some carbonic acid, take 

 place in the cells of the embryo, resulting in the solid 



