TilE PIIEXOMEXA OF GERMINATION. 
91 
THE PHENOMENA OF GJ,RMINATION. 
Substance of a Lecture at Chiswick Gaedexs. 
By Rev. Prof. G. Henslow, M.A., V.M.H., &c. 
[July 4, 1900.] 
The first point to be considered is the structure of seeds. A Pea, a grain 
of Wheat, and the seed of an Orchis may be taken as types. The last- 
mentioned is the simplest, inasmuch as the embryo is never complete, 
but remains arrested in the so-called " pro-embryonic " condition. In the 
Wheat the embryo is accompanied by a large mass of reserve-food 
materials called endosperm," which when ground makes flour. In the 
Pea all such food has been absorbed by the growing embryo itself 
during its formation, so that it has stored up its reserve food within the 
cells of the tissue of the two cotyledons or seed-leaves. 
These food materials usually consist of oil, starch or cellulose, and 
aleurone, the last being nitrogenous. 
The external conditions requisite for germination are the oxygen of the 
air, water, and a suitable temperature according to the nature of the plant. 
Also there must, of course, be an absence of noxious gases, as carbonic 
acid and other injurious substances, in the soil. 
When these external conditions are supplied, the reserve food, hitherto 
insoluble and unassimilable, becomes soluble by means of ferments 
secreted by the embryo, and especially by the epidermis of the cotyledon 
in contact with the endosperm when that is present. Thus, the ferment 
called diastase converts the starch into maltose and dextrin. Others 
convert oils into glycerine and fatty acids, and thence into starch. A 
third group attacks the aleurone and converts its various nitrogenous 
products into peptone and subsequently into assimilable amides, as 
they are called. In some cases the food consists of the greatly thickened 
and solid cell-walls themselves, as of a Date-stone. This has to be dis- 
solved in a similar way and then consumed. 
The ferments, or "enzymes," however, are accompanied by a most 
important function, that of respiration ; because the various processes 
carried on by the protoplasm depend upon the absorption of oxygen and 
its conversion into carbon dioxide by its union with carbon. The 
rationale of respiration is that some energy is required to decompose 
starch i^c, but this which is lost from the protoplasm is more than 
regained by the energy set free by the decomposing substances. The 
result is seen in the germination of the embryo. For a time they lose 
weight through the loss of carbon and water, but, of course, rapidly 
increase in weight as soon as roots and green parts are produced. 
As an illustration of respiration the following experiment may be 
mentioned. If a quantity of well moistened Peas be put in a closed glass 
jar in a warm place, they soon consume all the oxygen and replace it 
by carbonic acid. If, then, a lighted taper be quickly inserted it will go 
