302 LIFE : OUTLINES OF GENERAL BIOLOGY 



energy of their food into the kinetic energy of movement, usually 

 locomotor, the essential feature of plant-life is the utilisation of 

 food for increase in size and numbers. No doubt plants have their 

 varied outgo of matter and energy, as in the transpiration of water- 

 vapour, and in the transport from roots, through stem, to leaves; 

 and the loss of parts— such as foliage, flowers, and fruits; yet the 

 characteristic plant expenditure is in growth, 



NUTRITION. — The popular notion of plant nutrition seems to 

 this day too much inherited from that of Aristotle, with his un- 

 fortunate comparison of the plant to an animal burrowing for its 

 food in the ground, and so with its foliage merely like hair or plum- 

 age! In later times, even with clearer perception of the main task 

 of the roots, as for provision of water, the long persisting error became 

 questioned and at length put to an experimental test, crucial and 

 classic. Van Hclmont took a small willow twig and planted it in a 

 hu-ge pot of dry earth careful h' weighed, kept it supplied with rain- 

 water, and watched its growth year by year, until it was a little 

 tree. Carefully removing this, he found its weight many times 

 increased, yet the soil had only lost two ounces. Then, burning his 

 plant and weighing its ashes, he found the missing two ounces. 

 So he naturally wondered how came the plant by this enormous 

 increment? He then could but attribute this essentially to the 

 retention and transformation of part of the water he had been so 

 long supplying, and before the discovery of photosynthesis (nearly 

 a century later), this was wellnigh as far as he could go. But with 

 the recognition of the importance of the mineralconstituents, new 

 advances as towards the science and art of manuring became 

 possible- and are still in progress. 



The student still too commonly comes to the subject, if not even 

 with the old popular error, quite uninformed, or else is puzzled 

 by the later taught antithesis between the typical plant and the 

 animal which still survives too commonly. All ordinary animals 

 take in organic food, esjxicially proteins, carbohydrates, and fats: 

 all fungi, from mushrooms to moulds, and the common kinds of 

 bacteria do the same; parasitic plants such as dodder and broom- 

 rape absorb organic food from their hosts; and insectivorous plants, 

 like the sundew and the fly-trap, so far attain to the animsd level 

 of nutrition. Thus the student's difhculty is at once raised by the 

 frequent statement even in textbooks, let alone in school, that the 

 "food" of all ordinary green plants is inorganic, fundamentally con- 

 sisting of carbon dioxide and soil-water. This again is complicated 

 by the farmer's and gardener's way of speaking of manure as plant- 

 food— a conception again surviving from the Roman usage— (which, 

 indeed, actually deified manure 1), and with which European agri- 

 culture is so essentially continuous, since the modern teaching of 



