936 



THE NATURE BOOK 



one cotyledon carry the supply of food 

 material in a separate store, which is 

 spoken of as the albumen. The substance 

 set aside for the nourishment of the 

 seedling is sufficient to give the plant a 

 good start until it is able to set up house- 

 keeping on its own account. 



The seed lias been endowed with a 

 marvellous vitality, If the conditions are 

 not suitable for its development it can very 

 well wait until the circumstances are more 

 favourable. Thus, it is seen that the seeds 

 which fall to the ground in the autumn do 

 not, as a rule, germinate until the follcnv- 

 ing spring or summer. Well authenticated 

 instances are on record where seeds buried 

 deepty in soil have remained in a state 

 of suspended activity for many years. 

 Finally, when digging operations have 

 brought them more near the surface, they 

 have readily germinated, apparently little 

 the worse for their long confinement. 



SEED OF THE ELM IS SURROUNDED BY A WING-LIKE 

 EXPANSION. 



Granted certain conditions, the seed 

 will speedily show signs of development. 

 Warmth, moisture, and the presence of 

 oxygen soon stir the sleeping embryo 

 into life, and bring about the wonderful 

 changes connected with the birth of the 

 plant. Heat is necessary for the for- 

 warding of all vital processes ; moisture 

 is required for the conversion of the 

 nutrient into a fluid state, whilst oxygen 

 is necessary in order to bring about the 

 change of the starch into sugar, in which 

 form it can be assimilated by the plant. 

 In a chemical sense, starch and sugar 

 are not widely different, save that the 

 former contains an additional proportion 

 of carbon. The absorption of oxygen 

 by the seed sets free the carbon, and thus 

 changes the composition of the food 

 supply At first sight it may seem strange 

 that in the beginning sugar was not stored 

 away in the seed. It is a wise provision 

 that has ordered it other- 

 wise, for had sugar been de- 

 posited in the first instance 

 it would almost certainly 

 have undergone fermentation. 

 In this condition it would, of 

 course, have been useless for 

 the nourishment of the little 

 plant. 



The most obvious change 

 in the appearance of the seed 

 when conditions fav^ourable 

 for its germination are pre- 

 sent, is a decided increase in 

 size. This goes on apace until 

 the outer skin bursts, and two 

 very distinct parts are to be 

 seen. One, whitish in colour 

 and sometimes branched, 

 sinks at once into the soil — 

 tliis is the root ; the other, 

 of a light green shade, rises 

 above the ground — this is the 

 shoote In the germination 

 of the seed we are witness- 

 ing a phenomenon which has 

 provided the puzzle of the 

 ages. \\'hat is it that induces 

 the radicle with such per- 

 sistence to plunge into the 

 soil ? However the seed may 

 have been placed when it 

 germinated, the root always 

 wriggles round so as to strike 



