May 20, 1898.] 



SCIENCE. 



697 



coveries for which we are indebted to Mohl, 

 his claims to priority in them may justly be 

 disputed if this expression be taken to de- 

 note the pretension to have first seen or 

 spoken of a thing, * * * the lucid, con- 

 fident recognition of it is, however, due to 

 Mohl's observation." But in Sachs' case 

 the remark applies not merely to the obser- 

 vation of facts, to which Mohl confined him- 

 self, but to bringing into prominence the 

 importance of such facts in their relation 

 to the common stock of our knowledge, and 

 to the right ordering of observations in the 

 general building of knowledge — -work on 

 which he laid great stress. He writes : 

 " As I read your book I feel anew how 

 much more merit there is in working 

 out a comprehensive subject from reliable 

 sources, and from a higher standpoint, than 

 in constantly supplying fresh contributions, 

 which, however m^eritorious in themselves, 

 are yet as the scattered stones of the hillside 

 compared to milestones pointing us on our 

 way ! " 



Sachs is best known and most famous as 

 the founder of the modern physiology of 

 plants, and his physiological works may be 

 next touched upon. " My earliest treatises," 

 he once wrote, "were composed at a time 

 when the physiology of plants was simply 

 non-existent; I myself was entirely self- 

 taught and consequently much of my 

 work was imperfect, especially the manner 

 of exposition." Nevertheless these earlier 

 works are of great importance. ISText to be 

 named come his works upon chemical phil- 

 osophy. The investigations of Ingenhouss, 

 Th. de Saussure, Liebig, Boussingault and 

 others had supplied the foundation upon 

 which, in connection with the results of 

 plant-anatomy, a more exact knowledge of 

 the phenomena of metabolism was to be 

 built up. It was Sachs who first pointed 

 out "that the starch in chlorophyll is not 

 merely a secondary deposit, but must be re- 

 garded as the product of the assimilating 



activity (produced by the action of light) of 

 the granular, chlorophyll substance ; that 

 it is formed in the chloi'ophyll out of its 

 original elements, and is conducted to the 

 growing buds and to the tissues which store 

 up the reserve material " * — a brilliant addi- 

 tion to our knowledge, the fundamental 

 importance of which needs hardly to be 

 demonstrated at the present day. 



The formation of starch largelj' engaged 

 his attention later on. He contrived a 

 simple means of quantitatively estimating 

 starch-assimilation, and by the application 

 of the ' iodine test ' to leaves or portions of 

 leaves, respectively, supplied an extraordi- 

 narily simple and instructive method of 

 demonstration. 



His services in improving the culture of 

 plants in nutrient solutions are well known. 

 They drew down upon him a violent attack 

 from Knop which deeply wounded him, 

 and not without reason. It is now one of 

 the most elementary experiments in the 

 physiology of plants to rear a plant from 

 germination to seed-bearing by the admin- 

 istration of nutrient salts, but at that time 

 it was maintained that the seed-bearing 

 plants of maize must have been placed in 

 the solution of nutrient salts after they had 

 attained a flourishing condition ! 



He incidentally discovered the interest- 

 ing fact that polished marble slabs may be 

 corroded by roots — a fact of some impor- 

 tance for the understanding of the functions 

 of these organs. He began to work upon en- 

 tirely virgin soil when, at the close of his 

 fiftieth year, he set on foot investigations 

 which brought to light by microscopical 

 tests, and above all by microchemical meth- 

 ods, the movements, chemical changes, and 

 final consumption of the reserve material 

 during the growth of organs. These exper- 

 iments have also proved of fundamental 

 importance, and he lays stress upon the fact 

 that they served first to lead him to think 



* 'Collected Essays,' p. 335. 



