78 Inside the Living Cell 



cells. How this unity or continuity is maintained is still unknown. Dr 

 V. B. Wigglesworth put this point of view as follows : 



'What is the nature of this continuity which the cells are at such 

 pains to restore? May we not regard it as a chemical organism? On 

 this view the difference of organization of unicellular and multi- 

 cellular animals disappears. The latter, presumably for reasons of 

 size, are subdivided into cellular units. But we may picture the organ- 

 ism as a chemical continium; a prodigious molecule . . . with active 

 centres requiring specific hormones to enable them to exert their acti- 

 vity The cells do not "co-operate to mould the body form" — they 



merely carry and care for a small segment of the organism of which 

 they are the servants.' 



So we get glimpses of the organism as something more than a mere 

 collection of cells; but we do not know what the additional factors or 

 agents are. The whole organism is like a factory which is made up of 

 many specialized workshops, each having a task of its own. Into each 

 workshop or cell, raw materials come in and products are made and 

 sent out. But the factory as a whole is more than a collection of work- 

 shops; there must be planning and co-ordination which ensures that 

 everything works at the right rate. There must be services, supplies, 

 transport and flow sheets. 



Little is known of these 'organizers'. Substances which promote 

 growth have been isolated from plants and animals. Plant growth- 

 promoting substances called auxins were isolated by Kogl and are 

 of a comparatively simple nature. It was then found that quite simple 

 synthetic substances which may not exist in plants, such as deriva- 

 tives of indoleacetic and phenoxyacetic acids, also have this ability. 

 They are now manufactured on a large scale and used as selective 

 weed killers. This is because they cause dicotyledons to grow so 

 rapidly that some phases of the growth process outstrip others and 

 the plant dies. Another growth promoting substance is ghiberellic 

 acid, which, when introduced in extraordinarily small amounts, causes 

 dwarf varieties of plants, such as peas, to develop into giants. It does 

 this by stimulating the growth of cells in the direction of the stem. 

 The formation of flower-buds in plants is also controlled by chemical 

 substances. In many cases the formation of the flower-bud is deter- 

 mined by the length of the day, and not as we might think by the 

 average temperature. The flower bud is often formed during the 

 winter period and it has been found that a dark period of a certain 

 length is necessary at the time when flower buds are formed. If this 

 period is broken by a single flash of light, flowering may not occur. 

 In this case the formation of the flower bud is stimulated by a sub- 

 stance which accumulates in the dark. If the dark period is broken 



