JULIUS SACHS. 167 



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 

 organs are formed. The formation of blossoms was proved 

 to depend directly or indirectly 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 produc- 

 tion of flowers " seeks to define this phenomenon more 

 closely. 



The action of coloured light upon plants in respect to 

 assimilation and to their heliotropic curves, etc., received 

 soon after valuable 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 move- 

 ments of water in plants ". But even if his inbibition theory 

 be rejected it must not be forgotten how many valuable 

 facts are due to his activity in this field. The effects pro- 

 duced by the chemical and physical state of the soil upon 

 transpiration, the checking action of salt solutions, low 

 temperatures, etc., were well established ; the " Lithium 

 Method " was used for measuring the rate of the transpira- 

 tion current ; and the profound and far-reaching importance 

 of transpiration for the life of most plants was demonstrated. 



A further laborious and protracted series of experiments 

 dealt with the phenomena of growth and of movements 

 produced by stimuli. Among the more notable of these are 

 the construction of the first auxanometer, the graphic 

 description of his observations, and the recognition of the 

 grand period of growth. His investigations into the growth 

 of the main and side roots first proved convincingly the 

 factors which condition the regular extension of the root- 

 system in the ground, and established the distribution of 

 growth in roots, as well as the correlation between main and 



