SEEDS AND SEEDLINGS. 43 



2 litres (about 2 quarts) of carbon dioxide are given off. 

 If all this energy were used in mechanical work, it would 

 suffice to raise 3,400 kilograms through 1 metre (i.e. to 

 raise more than 3 tons a yard high). The energy is used up 

 by the plant in the form of heat and of chemical work, in 

 addition to mechanical work. 



74; Emergence of Seedlings from the Soil. You will 

 have noticed the way in which the plumule of the Bean pro- 

 tects the young leaves from injury by bending backwards at 

 the tip as it pushes its way upwards. Seedlings can grow 

 through hard and stiff soil, and in doing this the plumule 

 must exert considerable force. The shoot of a Broad Bean 

 seedling can push upwards with a force of over a pound, and 

 since its diameter behind the hooked part is about one-eighth 

 of an inch, the force exerted = 80 Ibs. per square inch. From 

 the fact that the cotyledons of a Broad Bean of average size 

 contain about a gramme of carbon, the seedling can get a large 

 amount of energy by using the stored food. 



* (a) Plant some Beans about 3 ins. deep in moist soil or sawdust 

 in a flower-pot, and pack stiff clayey soil (or plasticine) firmly above 

 them. Watch them to see whether they emerge at the sides or whether 

 they push the whole mass of clay upwards. 



75. Other Seeds and Seedlings. We have still many 

 experiments to make in our investigation of plant physiology, 

 and for a large number of these the seedlings of Broad 

 Bean, Scarlet Runner, and Sunflower, as well as others, will 

 be required. G-et seedlings ready in different stages of 

 growth. 



Meanwhile examine and germinate the seeds of various 

 other plants for comparison with those of the Broad Bean. 

 If you are really interested in Plant Life and have the neces- 

 sary time, you will find it worth while doing this with all 

 sorts of plants, both wild and cultivated. This easy and 

 interesting work with seeds and seedlings is perhaps un- 

 rivalled as a means of gaining an insight into the physiology, 

 adaptations, and evolution of plants, using only the simplest 

 apparatus and the cheapest materials the seeds of hun- 

 dreds of cultivated species can be bought in penny packets. 



