MOLECULAR STEUCTUEE AND LIFE — PICTET. 203 



ucts through which this takes place. These are the formic and 

 glycolic aldehydes, sugars and starch, numerous vegetable acids, 

 asparagin, glycerin, fats, lecithins. These substances exist in all 

 plants. They are found in each living cell, together with the pro- 

 teins which are essential constituents of protoplasm. They rightly 

 appear then as the foods of this cell. 



However, if the constitution of these bodies be considered, the fact 

 is striking that their molecules are made up only of open chains of 

 atoms. None of them shows the cyclic structure. There is thus ob- 

 served a fundamental relation between the constitution and the role 

 of vegetable substances. All those that may be legitimately consid- 

 ered as the direct and successive products of assimilation, all those 

 that contribute to the building up and nourishment of living proto- 

 plasms, belong to the first class of organic compounds. 



But these substances are far from being the only ones that the 

 vegetable kingdom furnishes us. Besides these the plant produces 

 an infinite variety of others which human industry constantly 

 searches for, not only to utilize them as foods, but also to profit by 

 any of their other properties. Thus, for example, the great group 

 of essential oils, turpentines, and camphors, many representatives of 

 which constitute our perfumes or our highest prized condiments. 

 There is also the long series of colorants and vegetable pigments, 

 from chlorophyl to that interesting group of anthocyanins, or flower- 

 pigments, the systematic study of which is being taken up by our 

 former colleague, Willstatter. There are the various resins, the 

 rubbers, the tannins, the glucosides, the various bitter or astringent 

 principles. Finally, there are all those numerous nitrogenous and 

 basic compounds grouped under the name of alkaloids and which, 

 chiefly, because of their remarkable physiological action in the ani- 

 mal organism, have furnished our most valuable medicines. Is 

 the part that these substances play in the plant the same as that 

 of compounds of the first category? It is generally believed other- 

 wise. And yet many physiologists still accept it to-day and see in 

 these substances reserve food materials that the plant will utilize 

 when the time comes to build up its tissues. 



I do not at all share this view and for the following reasons : 

 These substances seem to me not at all like the first, that is, indis- 

 pensable to the development of plants, since many plants do not have 

 them. They are not found, as are the others, inclosed in the seeds 

 or in the roots. They are never met with in the li\ing cell, from 

 which they seem to be excluded, but are mainly in the tissues or in 

 special receptacles where they are localized and stored separate from 

 the great tract of protein formation. They do not disappear but 

 on the contrary are accumulated during the life of the plant. They 



