Its Structure tn Animals, and Grovoth. 7 



is centred in the man who designs and makes a watch, and not in 

 the watch itself. We may speak of a plant, an animal, or a mass 

 of protoplasm as a machine if we please, just as one may style the 

 cells of plant leaves laboratories because in them chemical processes 

 are carried on, or as we may say that the leaves themselves are 

 the lungs of the plant because chiefly by them the plant is able to 

 breathe ; but this is figurative language. 



And if we call a plant a machine, let us recognize how much 

 superior such a machine is to the most perfect one constructed by 

 man, for it supplies itself automatically with the means to produce 

 the energy necessary for its growth, development, and perfect 

 action, and it gives birth to other machines of the same kind as 

 itself which shall take its place when it is worn out and dead. 

 Engineers build wonderful and powerful locomotive and other 

 engines, but they have constantly to supply water to the boiler 

 and coal to the furnace or their machines would stop working. 

 Horologists construct watches and clocks, but to keep them going 

 they have to be wound up from time to time, and electricians 

 establish telegraphs, but their batteries have continually to be 

 renewed ; while these and all other man-made machines wear 

 themselves out without producing anything to take their place. 

 Growth. 



Every botanist who has paid any attention to the physiology 

 of the plants he studies, knows that the carbon in the molecules 

 of the protoplasm is abstracted by composition with the oxygen 

 breathed in through the stomates of the leaves or the lenticels of 

 the stems, and that so necessary is this respiratory process to the 

 very existence of all tissues and cells in every part of the organism, 

 that even roots of plants such as mangroves growing in mud, 

 where the supply of oxygen is not equal to their demand, send up 

 erect branches into the air, where they form pneumathodes or air 

 openings, and that other plants such as our native Epilobium hir- 

 sutum, Lythrum salicaria, and Lycopus europ&us, in order to meet 

 the scarcity of air in wet soil, form at the base of their stems a 

 special white, spongy tissue for their adequate aeration. The 

 resulting compound of carbon and oxygen is breathed out through 

 the stomates, and thus the protoplasm loses substance and weight. 

 Other compounds, the products of metabolism, either of no obvious 



