102 CHEMICAL HISTORY OF GERMINATION. 



and its conversion, by torref action, into the substance called 

 British Gum, which, in common with other varieties of amyla- 

 ceous matter resulting from the action of heat upon starch, has 

 lately received the chemical appellation of Amidine. The 

 varieties of Starch and Amidine used as articles of food were 

 described, and specimens of them exhibited: these include, 

 among others, Indian Arrow-Root, which is a pure starch, 

 prepared from the root of the Marantha arundinacea ; Sago, 

 obtpined from the pith of an East Indian Palm-tree, and Ta- 

 pioca, from the root of a South American plant, the latropha 

 Manihot) both which exist in the form of starch in the plants 

 themselves, but are more or less converted into amidine by 

 the heat employed in their manufacture. The vegetable prin- 

 ciples called Gum and Gluten were then mentioned, the gum 

 of the Acacia, termed Gum Arabic, and the gluten of Wheat, 

 being taken as examples of them. 



An important object of this Course was to explain the 

 changes which either take place with, in nature, or are artifi- 

 cially induced upon, the chemical principles of vegetation, by 

 alterations inr the proportions or in the arrangement of their ul- 

 timate constituents. It was commenced, accordingly, with the 

 general view of the chief nutritive elements of vegetable matter, 

 of which the foregoing is an epitome. Having thus prepared the 

 way, the Physiological and Chemical history of Germination 

 was entered upon. The chemical principles of seeds already 

 described being again enumerated, the structure of seeds 

 (chiefly of the Dicotyledonous class) was explained, enlarged 

 drawings of the epidermis or outer skin, the cotyledons or seed- 

 lobes, and the germ, being exhibited in illustration, and each of 

 these parts being demonstrated in actually germinating seeds. 

 It was shown by these means, that the office of the radicle of 

 the germ was to descend into the earth and form a root, that of 

 the plumula of the same organ, to rise into the air and expand 

 into stem and leaves; and that of the cotyledons to supply the 

 young plant so produced with nourishment. A view was then 

 taken of the conditions which are necessary in order to enable a 

 seed to germinate, with respect to the presence of moisture and 

 of oxygen, and to the preservation of a certain temperature, 

 various facts being related in illustration of each condition, 

 and the history of our knowledge on these points briefly traced. 

 The changes in the condition and structure of the seed, which 

 constitute germination, were next pointed out, as well as the 

 chemical changes undergone by the substance of the cotyle- 

 dons, consisting, essentially, in the conversion of the compara- 

 tively insoluble and innutritious starch which they contain 

 into soluble and nutritive sugar , which is supplied to the grow- 



