GROWTH. 105 



If the season of the year is one that will permit, make some 

 observations on the force exerted by seedlings in coming through 

 the hard earth; of mushrooms coming up through dry and 

 hard earth; of the wedging of roots in the crevices of rocks. 

 Or recall and note any observations of this kind made in the 

 past. One has only to note the immense size and weight of 

 some trees to understand the force which must have been ex- 

 pended during their growth in lifting up the food materials for 

 these massive objects. 



181. Energy of growth. This is manifested in the compara- 

 tive size of the members of a given plant. To take the sun- 

 flower for example, the lower and first leaves are comparatively 

 small. As the plant grows larger the leaves are larger, and this 

 increase in size of the leaves increases up to a maximum period, 

 when the size decreases until we reach the small leaves at the 

 top of the stem. The zone of maximum growth of the leaves 

 corresponds with the maximum size of the leaves on the stem. 

 The rapidity and energy of growth of the stem is also correlated 

 with that of the leaves, and the zone of maximum growth is 

 coincident with that of the leaves. It would be instructive to 

 note it in the case of other plants. 



Exercise 38. 



182. To study zone of maximum growth. Study the zone of maximum 

 growth in several plants which may be at hand. Some plants may be ob- 

 tained for use from conservatories. Other plants may be collected during the 

 growing season and preserved for this purpose. Corn plants, for example, 

 can be gathered at maturity in the early autumn or late summer. They 

 may be carefully pressed entire, and mounted on large sheets, or on paste- 

 lx>;ml. The zones of maximum growth of the stem as well as of the leaves 

 can be studied from these preserved plants. The plants in this condition 

 will serve this purpose for several years. 



For other experiments and studies on growth see the author's 

 larger ' ' Elementary Botany. 



