41 



an egg (which is rich in nitrogen), but the plant being unable to obtain its 

 nitrogen from the atmosphere, obtains it from ammonia, i.e., from hydro- 

 gen and nitrogen in combination — and such substances are found in 

 organic matter. Part of the structure of the plant, it was shown, 

 is built up from the in-organic particles of the soil ; manure supplies 

 the organic want of the plant in the form of nitrogen, also the in-organic 

 elements in a soluble state. These in-organic elements in the plant are 

 left in the ash when the plant is burnt, the organic on the other hand 

 are consumed. 



Mr. Dowker, said he wished to place the complicated phenomena 

 of plant structure in a popular way before his audience ; and 

 in reference to the organic substances which were known as plant 

 products, such as cellulose, starch, sugar, gum, plant gelatine, he 

 explained that they were all composed of the elements, carbon, hydrogen, 

 and oxygen, and in chemical language were expressed by a formula, 

 C 12, H 10, 10 ; and that these substances can be converted one into 

 the other by varying the proportions. He compared the difference 

 rouglily to three dice which may be shuf&ed in a box and come out six, 

 three, or two, as it may happen. In the plant the proportion of each 

 was regulated by the protoplasmic contents of each cell, in a wonderful 

 way which we cannot comprehend. 



The structure of the wheat straw and leaf was next shown ; and 

 the tubular form of the straw, strengthened as it was by a deposition of 

 silica, instanced as a wonderful provision of nature to secure the 

 greatest strength combined with the least expenditure of material. 

 Having dwelt upon the additions to the plant during its growth, 

 Mr. Dowker next drew attention to its maturity and provision for the 

 continuance of the species by the formation of seed. 



As summer advances heat and light increase, and a corresponding 

 impetus being given to the plant its energies are now directed into a 

 different channel. Instead of leaves the ear is produced, and in it the 

 ovule or ovary and the stamens. These stamens have three filaments, 

 and the anthers are provided with fructifying pollen. In some plants 

 provision is made for cross fertilization by insect agency, but in the wheat 

 this is effected by the wind, which blowing across the field causes those 

 undulatory motions we call waves of the corn, and the action transfers the 

 pollen of one plant to the ovary of another. It was pointed out how 

 important it was for the wheat crop that it should have a fine time for 

 blooming, that this dusty pollen might be thus distributed. Up to 

 this time the plant's energies have been drawn towards the growing 

 parts, and stores of plant material, chiefly starch, have been deposited 

 in the matured tissues. The stimulus of the growing shoots too have 

 been the means of drawing its growth in that direction. Xow a new 

 stimulus is applied, while the other remains dormant. This new 

 action causes the absorption of the nutriment hitherto bestowed 

 upon the stem and leaves, and re-distributes it in the maturing grains. 



