166 SCIENCE PROGRESS. 



of the problem and went far towards clearing it up. 

 Even more important were " The Physiological Experi- 

 ments upon the Dependence of Germination on the Tem- 

 perature ". For by these the law of the " drei Kardinal- 

 punkte " (three cardinal points) was established, and the 

 term " Optimum " introduced for one of them — a name that 

 has been adopted in other departments 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 manual dexterity and skill in devising 

 simple, but extremely effective, 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 establish- 

 ment of the fact that not only light, but at the same time a 

 sufficiently high temperature is needed for the formation of 

 chlorophyll in the higher plants, was of great interest. 



From amongst the series of researches grouped together 

 in the Gesammelten Abhandlungen {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 Development of Different 

 Plant-organs ". 



The fact that the formation of cells and organs is depen- 

 dent upon light was submitted in this paper for the first 

 time to a searching investigation ; it was shown that the 

 formation of roots was in many cases directly favoured by 

 light ; the conclusion was drawn from Wigand's data that 

 with fern prothallia light determines the dorsiventrality, and 

 the phenomena of etiolation, which still present many enig- 

 mas, 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 Tropaeolum, Brassica, etc., continue to produce etio- 

 lated stem-parts and leaves in darkness " in sufficient quan- 

 tity for the production of fresh blooms if this depended only 



