8 WORCESTER COUNTY Hf)RTICULTURAL SOCIETY. [1879 



stems under and above ground, leaves, and seeds. It is used 

 for many purposes, chiefly the following : making wood, and the 

 like, building up new parts, forming flowers, and making seeds. 

 To sum up the work of green tissues, whether on the stem 

 or in leaves themselves, it may be said that they lift dilute 

 solutions from the roots to the light and air, there concentrating 

 them ; that they are the factories where starch or something 

 very similar is made." 



[The effect of plants on the air of rooms, and the relation of plants to 

 poisonous gases in the air of cities, were described at considerable length. 

 Wardian cases and window gardening were also treated of.] 



" When the trunk of a tree or the stem of an herbaceous 

 plant is carefully burned in the open air, there remains behind 

 a certain amount of rusty-gray ashes. This substance repre- 

 sents the mineral matters taken in solution by the roots, and now 

 changed somewhat by combustion. Some plants contain more 

 of this mineral matter than do others, but all of them have a 

 trace ; and there is a substantial agreement in the chemical 

 elements of the ash of different plants. Some of the elements 

 which have been detected in the ash are Iron, Potassium, Cal- 

 cium, Magnesium, Phosphorus, and Sulphur. These exist in 

 composition in the ash, — for instance, the Potassium is there a 

 carbonate ; but as to the manner in which they existed in the 

 plant, and how they were there compounded, authors are not 

 exactly agreed. Nor is it precisely known what part each plays 

 in the life and health of the plant. There is good reason for 

 believing that Iron is indispensable to the efificiency of chloro- 

 phyll, and that the salts of Potassium have much to do with 

 the production of starch. ' Besides the substances just men- 

 tioned, some compound of Nitrogen is essential to the growth 

 of plants ; and this is furnished, likewise, through the roots. 

 If, therefore, it is desired to have plants grow in a healthy and 

 vigorous manner, they must not only be placed under the requi- 

 site physical conditions, but good food in proper amount must 

 be furnished. 



Plants, as we have already seen, obtain their carbonic acid of 

 the atmosphere. The soil furnishes other kinds of matter used 

 as plant-food. To show how small a part is taken in certain 

 cases by the mineral constituents of plant-food, it may be well 

 to call to mind one of the earliest experiments upon the subject 

 of vegetable nutrition. Van Helmont placed in a proper recep- 

 tacle exactly two hundred pounds of carefully dried soil, and 



