26 ST0DY OF COMMON PLANTS. 



' in order to spend on one side, Nature is forced to econo- 

 mize on the other side.' " ^ A considerable number of 

 seeds, notably those of certain plants belonging to the 

 mustard family, have one cotyledon larger than the other, 

 an arrangement naturally following the way the embryo 

 is packed in the seed. These and various other peculiar- 

 ities may be seen in the embryo before germination, but 

 are more pronounced in the young seedling. 



During germination the reserve materials stored in or 

 around the embryo are drawn upon for the sustenance 

 „ of the seedling. Microscopic examination of 



Changes ° '^ 



in reserve the endosperm of a grain of wheat or Indian 

 materia s. corn, after the seedling is well started, shows 

 that the starch granules have undergone remarkable 

 changes due to the action of a ferment that gradually 

 dissolves them. Other reserve materials, such as oil, 

 aleurone, etc., undergo similar changes, by which they 

 are fitted for absorption, but these are too complicated 

 to be discussed in an elementary work. Those interested 

 in the chemistry of germination should consult Sachs, 

 Physiology of Plants, and later articles in various botan- 

 ical periodicals. 



Certain external conditions are essential to germination. 

 Of these the most important are (1) a suitable amount of 

 Conditions of water, (2) proper temperature, and (3) access 

 germination, gf oxygen. Simple experiments are easily con- 

 ducted to establish these facts, which are' also, in part, 

 matters of familiar observation. Thus when a crop of 

 grain has been sown it is well understood that it will not 

 come up if the earth is too dry, and that it is more likely 

 to decay in the ground than to germinate if it is too wet, 



1 Cf. Darwin, Power of Movement in Plants, pp. 94, 98 ; Lubbock, 

 Seedlings, II, p. 6. 



