130 GENERAL BOTANY 



Movements. During these various internal activities the 

 external organs of the growing plant are actively engaged in 

 adjusting themselves to the environment ; but this indispensable 

 phase of the plant's life has already been dwelt upon at suffi- 

 cient length and need not be reviewed at this point. 



SUMMARY 



We see, therefore, that during its brief seasonal life the bean 

 plant carries on a complex series of physiological activities quite 

 comparable to those maintained by the bodies of animals and human 

 beings (Fig. 63). Water and crude salts are absorbed from the soil 

 by osmosis and are transported through specially differentiated ducts 

 to the manufacturing mesophyll cells of the leaves. Carbon dioxide 

 and oxygen stream in through stomata, circulate through the intercel- 

 lular spaces, and are absorbed by the living cells for food construction 

 and respiration. Food is made by photosynthesis and is temporarily 

 stored during the day in .the leaf cells ; this food is then digested 

 at night by active digestive ferments and is transported through the 

 phloem and wood rays to points of special activity in growth or to 

 permanent storage tissues in the seeds. Respiration and assimilation 

 are always going on in all living tissues day and night, but they are 

 especially active in floral parts during the period of their formation 

 and in the germination of seeds in spring. The seeds are the special- 

 ized resting and wintering portions of bean plants which are adapted 

 to carry the plant over inclement periods for which the more delicate 

 working plant body is unfit, and in them, therefore, rests the assur- 

 ance of a new generation of bean plants in each successive season. 



A BIENNIAL: THE WHITE SWEET CLOVER 



If we compare a biennial plant like white sweet clover with 

 that of the annual bean plant described above, we shall find the 

 seasonal and physiological history of the biennial quite different 

 from that of the annual. The general physiological processes con- 

 cerned with seed germination, the absorption and movement of 

 water, photosynthesis, and respiration will be similar in the two 

 plants ; but the seasonal history and the handling and storage 

 of foods are quite unlike in the two, on account of the biennial 



