CHAPTER XXIV 

 CONCLUSION 



In the foregoing chapters we have become acquainted 

 with some facts about living beings, especially plants, 

 and we may now briefly consider the chief lessons 

 about life that we learn from them. 



In the earlier chapters we saw. that life everywhere 

 depends uppn a substance we call protoplasm — ^that 

 this is present wherever we find life — ^in 3.II organisms 

 from amoeba to man, and from bacteria to the seed 

 plants — and that it is not present in lifeless objects. 

 This protoplasm, as we saw, has a more or less definite 

 chemical constitution. It is not itself a chemical 

 compound, but a mixture made up in all organisms of 

 the same classes of compounds. In physical structure, 

 too, it is everywhere similar, belonging to a kind of 

 substance — or rather a special condition of matter 

 known as the colloid condition — which consists of very 

 minute particles or droplets of one substance (disperse 

 phase) dispersed through a continuous medium (con- 

 tinuous phase) of another. When the continuous phase 

 of a colloid is a liquid such as water the colloid is 

 called a sol, and certain sols as the result of the loss 

 of water, or of other causes, pass into a jelly-like 

 conditon known as a gel, in which the disperse particles 

 are more aggregated, though there is no sharp limit 

 between the sol and the gel conditions. 



Protoplasm, as we saw, is a mixed colloid sol or 



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