CHAPTER IV 

 GROWTH OF PLANTS 



26. Growth of Plants. Germination of Seeds.— One of the 

 most important manifestations of the vital activity of plants 

 is their growth, their continuous increase in size. 



Growth is closely connected with the formation of new cells, 

 tissues, and organs of plants as well as with the increase in volume 

 of the cells. Any reversible increases in volume, resulting, for 

 instance, from the swelling of seeds in water, are not considered 

 as growth. Growth is usually combined with a corresponding 

 increase in the total mass of the plant, but there are cases where 

 growth is accompanied by an expenditure of substance. For 

 instance, during the first stages of germination of seeds or the 

 utilization of reserves from storage organs when the leaves have 

 not developed, there may be observed considerable losses of 

 organic substances due to respiration, but new cell formation 



occurs. 



In such cases, the total increase in the size of the seedlings takes 

 place on account of the water absorbed during new cell formation 

 with the translocation and use of substances for new cell struc- 

 tures. Swelling that predominated in the first stages of germina- 

 tion is later supplanted by the increased water-holding capacity 

 of structures formed during the growth of new cells. On drying 

 germinated seedlings, it will be observed that there is a decrease, 

 not an increase, in dry substance, which may amount on pro- 

 longed germination to over 50 per cent of the initial weight of 

 the seeds. In this case, the growth of seedlings is combined not 

 with an accumulation but with a redistribution of organic 

 substances. Organic substances that have been stored during 

 ripening of the seed are partly used for the creation of protoplasm 

 as well as for laying down the walls of the newly formed cells; 

 they are consumed, also, to obtain the energy necessary for 

 growth. 



These two opposite functions, the consumption of reserves and 

 the creation of new tissues, which characterize germination and 



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