100 



potato, bacon and beans ; bread, bacon and eggs. It was 

 customary in former days always to put little cubes of bacon in 

 pea-soup ; for peas, beans, lentils and other members of the same 

 "leguminous" family are very highly nitrogenous, containing 

 about 22 per cent, of albuminoids, while potatoes contain about 

 2 per cent. ; on the other hand the peas have 51 per cent, of .starch. 

 It may be added that too great a deficiency in any one of the three 

 is injurious. It is said that " beri-beri " is caused by too great 

 a rice-diet, this grain being very deficient in nitrogenous sub- 

 stances, 7.5 per cent., starch being 76; while wheat has 1 1 of 

 albuminoids and 69 per cent, of starch. We have now had a 

 general survey of carbon as widely present in plants, but always 

 in combination with other elements. It only becomes visible as 

 a mineral when turned to charcoal or soot. 



We must now consider how the energy is supplied to Life 

 w r herewith all these compounds are made, just as we cannot use 

 an engine unless coal is burnt or some other source of force can 

 be utilised, as a waterfall, from which the force of gravity is 

 extracted. 



The process of respiration is the same, but in a much milder 

 form, as burning. In a candle the carbon of the wax or tallow 

 is " burnt," i.e., when heated it unites with the oxygen of the 

 air and thus forms carbonic acid, gas, which is so hot as to be 

 coloured red or yellow and makes the flame, while water is given 

 off at the same time. This is easily shown by putting a cold, dry 

 metal spoon just over the tip of the flame, when dew appears and 

 momentarily rests on the outer surface of the bowl of the spoon. 



To supply energy in plants, a carbo-hydrate is usually taken 

 and decomposed by the plant, with the aid of oxygen from the 

 air, into carbonic acid gas and water, while the energy, originally 

 absorbed from the sun's rays in the formation of the carbo-hydrate, 

 is liberated and is at the disposal of Life wherewith to carry on 

 all its vital functions. The chief stimulus to respiration is heat, 

 or the obscure rays beyond the red in the solar spectrum. 



By plotting out in a curve the increase of CO-§ by respiration 

 with the corresponding degrees of heat appl'ed, it is found that 

 the curve becomes a parabola, that is, the same curve as a stone 

 will take if thrown up into the air. It is a continuous curve, 

 so that it seems to show that the only limit would be death to 

 the plant if the heat be too strong, as practical experience tells 

 us is the case. 



Burning and respiration are thus seen to be practically the 

 same thing ; the effect in both animal and vegetable kingdoms 

 is the same — the liberation of energy for life-work. 



Now let us turn to the use to which plants put their cells. 

 At first, as in herbs, there is much soft cellular tissue usually 

 charged with water for the plant's use ; while in some tropical and 

 other countries, with situations of great drought in which plants 

 have to tide over rainless periods, cellular tissue is converted into 

 water-storage reservoirs. Thus the curious massive forms of 



