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SCIENCE. 



[N. S. Vol. VII. No. 177 



that the chlorophyll grains are the true or- 

 gans of assimilation. A bare reference 

 must suffice to the classical treatises on the 

 germination of the date-palm, of grasses, 

 or on inulin, etc. 



In later years he ceased to contribute ex- 

 perimentally to our knowledge of metab- 

 olism. Other problems had meanwhile 

 claimed his attention. His investigations— 

 the first to be made— into the action of heat 

 claim special notice. The phenomena of 

 freezing had long been in need of investiga- 

 tion, and here also Sachs' work created a 

 clear conception of the problem and went far 

 towards clearing it up. Even more impor- 

 tant were ' The Physiological Experiments 

 upon the Dependence of Germination on the 

 Temperature.' For by these the law of the 

 ' drei Kardinalpunkte ' (three cardinal 

 points) was established, and the term ' Op- 

 timum ' introduced for one of them— a 

 name that has been adopted in other de- 

 partments of science. These experiments 

 were carried out with the simplest appliances 

 not even in a botanical laboratory, but in 

 his own rooms at Prague. His great man- 

 ual dexterity and skill in devising simple, 

 but extremely eifisctive, instruments were 

 most useful to him. 



The discovery that with sensitive organs 

 there are temporary conditions of rigor due 

 to heat and cold has become an intrinsic 

 part of physiology, whilst the establishment 

 of the fact that not only light, but at the 

 same time a sufficiently high temperature, 

 is needed for the formation of cholorophyll 

 in the higher plants was of great interest. 



From amongst the series of researches 

 grouped together in the Gesammelten Abhand- 

 lungen ( Collected Essays) under the heading 

 ' The Action of Light ' I should like shortly 

 to refer to the treatise ' Upon the Influence 

 of Daylight on the Production and Devel- 

 opment of Different Plant-organs. ' 



The fact that the formation of cells and 

 organs is dependent upon light was sub- 



mitted in this paper for the first time to a 

 searching investigation ; it was shown that 

 the formation of roots was in many cases ' 

 directly favored by light ; the conclusion 

 was drawn from Wigand's data that with 

 fern prothallia light determines the dorsi- 

 ventrality, and the phenomena of etiolation, 

 which still present many enigmas, were 

 more closely examined. The investigation 

 into the action of light through the medium 

 of the foliage-leaves upon the formation of 

 flowers was especially important to Sachs, 

 because it formed the starting-point for his 

 later theory of ' Matter and Form.' It 

 showed him that plants, such as TrojMeolum, 

 Brassica, etc., continue to produce etiolated 

 stem-parts and leaves in darkness " in suf- 

 ficient quantity for the production of fresh 

 blooms if this depended only upon the bulk 

 of the material stored for the purpose and 

 not also upon the particular quality of it," 

 a fact that later led him to form his theory 

 as to the specific matter out of which or- 

 gans are formed. The formation of blos- 

 soms was proved to depend directly or in- 

 directly upon light, inasmuch as by the 

 assimilating activity of the leaves in light 

 the materials destined to produce flowers 

 are formed. Later research into ' The action 

 of the ultra-violet rays upon the production 

 of flowers ' seeks to define this phenomenon 

 more closely. 



The action of colored light upon plants 

 in respect to assimilation and to their helio- 

 tropic curves, etc., received soon after valu- 

 able confirmation. Sachs introduced the 

 simple and convenient method of counting 

 the bubbles given off by water plants in 

 light, and came to the conclusion (which 

 lately has again been questioned) that the 

 so-called chemical rays have very little to 

 do with the giving off of oxygen. 



A keen controversy was aroused by the 

 opinions he formed in consequence of his 

 researches into ' The movements of water 

 in plants.' But even if his inhibition 



