HYDROCARBONACEOUS SUBSTANCES. 63 



matters takes place in the act of vegetation, in all probability by a meta- 

 morphosis of starch or sugar already formed. This is the origin of 

 fatty matters generally recognized by vegetable physiologists. In this 

 change the proportions of carbon and hydrogen are increased 50 or 60 

 per cent., while that of the oxygen is largely diminished. By itself, 

 accordingly, it would be a reducing process, similar to that by which 

 starch is first formed from inorganic matter. But this is not the view 

 usually entertained in regard to it. The deoxidation of carbonic acid 

 and water can take place, so far as we know, only in the chlorophylle- 

 holding cells of the plant ; and fatty matter is often produced, as in oily 

 seeds, where no chlorophylle is present. It is possible that the reduc- 

 tion of the quantity of oxygen, during the conversion of starchy mat- 

 ters into fat, may be accompanied by the liberation of carbonic acid, 

 and the formation of other highly oxidized substances, which would 

 account for the diminished proportion of oxygen remaining. Some- 

 thing of this sort takes place in the alcoholic fermentation of glu- 

 cose, already described (page 57), as follows: 



GLUCOSE. ALCOHOL. CARBONIC ACID. 

 C 6 H i2 6 = 2C,H 6 O -f 2CO 2 . 



Here the alcohol produced by fermentation contains a smaller pro- 

 portion of oxygen than the original glucose ; but another body (car- 

 bonic acid), containing a larger proportion, has been liberated at the 

 same time. The missing oxygen therefore has not been discharged in 

 the free condition, but in a more stable form of combination than be- 

 fore. A similar change taking place in the starchy or saccharine matters 

 of a plant, with the production of fat, would not be altogether a deoxi- 

 dation, but would include a rearrangement of the chemical elements, 

 with the simultaneous production of other compound bodies. 



There are no means at present known by which the transformation 

 of starch into fat can be artificially accomplished, and even its chemical 

 formula cannot be expressed with any reasonable certitude. But there 

 are well-known facts which make it highly probable that such a change 

 may be and is effected in the tissues of the living plant. In the first 

 place, it is certain that starch disappears from the leaves in which it is 

 produced, to be transported under a soluble form to other organs. 

 Secondly, there are instances of the production of oily seeds, or other 

 fatty reservoirs, in plants where no other deposit than that of starch 

 can be detected in their chlorophy lie-holding leaves.* And, thirdly, 

 the oily seeds of certain plants while still immature contain starch, but 

 as they ripen the starch diminishes or disappears and oil takes its place. f 



Varieties of Fat. The most important and abundant varieties of 

 fat are Stearine, Palmitine, and Oleine. They resemble each other in 

 general character, and differ mainly in their degree of consistency, 

 stearine being the most solid at ordinary temperatures, while palmi- 



* Mayer: Agrikultur Chernie. Heidelberg, 1871. Band I., p. 86. 

 f Johnson: How Crops Grow. New York, p. 94. 



