252 METAMORPHOSIS 



whole are they capable of performing their functions adequately, and only then 

 is it possible for the whole structure to grow and thrive. In this way we can 

 see that correlations become established among the various parts, one essential 

 result of division of labour. These correlations have, however, a much 

 greater influence on the general shape of the plant than we might conclude 

 from these remarks. 



Numberless correlations make their appearance if members be isolated, if 

 leaves, branches, or roots of plants be separated off and prevented from rapid 

 decay by appropriate artificial means. The capacity for regeneration then 

 makes itself apparent, that is to say, the capacity of a member to reconstruct 

 the whole body by budding out the missing organs. The root can give rise to 

 shoots, the shoot to roots, the leaf to both shoot and root. The normal plant 

 gives us no hint of this power, and yet that power must have been latent in it ; 

 the inter-relationships of the members only must have prevented the individual 

 organs from exhibiting all the capacities which they possess. Owing to this cor- 

 relation the growth and formative power of the different members are regulated 

 and made subservient to the whole in such a way that the structural evolution 

 which we are accustomed to see in the plant proceeds harmoniously. What is 

 true of the root and shoot as a whole is true also of the individual cells. Num- 

 berless myriads of parenchymatous cells die off at last when they have reached 

 a certain stage in development and after they have lived a long time in that 

 stage. They can all be induced to form every possible kind of cell by inhibiting 

 correlations, and hence may be made to continue alive for indefinite periods. 

 If this subordination of cells did not exist in the multicellular plant each cell 

 would endeavour to develop as much as it could, and then we should have not 

 an organism but such a chaos run wild as to make existence impossible. 



The flowering plants are perpetually altering their shape, and the organs 

 to which they give rise are not only so far adapted that they perform the 

 specific functions which enables them to carry out their structure, but also in 

 so far that they do not exhibit all the activities of which they are capable. 

 The entire life-cycle of the plant from the germination of the seed to the 

 formation of seed takes place under constant external conditions, so that we are 

 unable to refer these changes in shape to these factors with the same degree of 

 accuracy that we did in the case of Basidiobolus. Nevertheless, this life-cycle 

 is affected by external influences, and that, too, in a double sense. 



Whenever a seed gives rise to a seedling the first thing it requires is a certain 

 amount of water ; that is self-evident, since we have seen that water is an 

 absolutely essential constituent of the living organism. Since the seed in a state 

 of rest is quite air-dry, the addition of water is necessary to awaken its activities. 

 If a member of a plant has accumulated a store of water during its resting 

 period it is able to start developing without any such addition. But not only 

 must water be absorbed, it must also be immediately available if growth is 

 to be effected, and the same is true for all other substances needed for this 

 purpose. They must be absorbed, or have been absorbed previously, and 

 in that respect every growth phenomenon in a plant is dependent on the 

 external world ; this, however, requires no further elucidation it is self-evident. 

 The influence of temperature on development is not so obvious. Yet a glance 

 at re-awakening nature in spring time indicates to us what part temperature 

 plays in vegetative phenomena. Experiments confirm this and show that the 

 carrying out of every individual function in the plant is dependent on the 

 existence of a certain amount of heat. Beans first show evidence of growth 

 when the temperature reached 9 C. ; growth increases as the temperature rises 

 (up to 34 C.), and finally ceases when 46 C. is reached. Three cardinal points 

 of temperature, a minimum, optimum, and maximum, may be established 

 for all organisms, and the very diverse positions of these cardinal points indicate 

 the varied requirements of organisms as regards temperature, and at the same 



