1] 



UPON THE RATE OF GROWTH 



315 



plants. Whether non-chlorophyllaceous plants can make use 

 of it has been much discussed, and is worthy of further inves- 

 tigation. WINOGRADSKY ('88, '89) has, indeed, shown that 

 the sulpho-bacteria store up pure sulphur from sulphuretted 

 hydrogen (H 2 S), and PRESCH ('90) has concluded, as a result 

 of feeding himself with pure sulphur and analyzing the sulphur 

 of the urine, that about one-fourth of the sulphur taken into 

 the body in an elementary form becomes built up into organic 

 molecules. Recently HERBST ('97) has shown that embryos 



lays 



No 

 3 days 



FIG. 87. Right, Larva of Echinus reared for 72 hours in water containing all the 

 necessary salts ; the sulphur being in the form of 0.26% magnesium sulphate and 

 0.1% calcic sulphate, and the phosphate in the form of CaHPO 4 . The larva is 

 normal. Left, Larva reared for fi8 hours in a solution containing no sulphur nor 

 CaCl 2 . The typical larva without sulphur, but with CaC1.2, differs from this chiefly 

 in the presence of rudimentary spicules ; kr, spicule-formiug cells. (From HERBST, 

 '97.) 



of sea-urchins and other marine animals do not develop in the 

 absence of sulphur (Fig. 87). These facts indicate that not 

 green plants merely, but all organisms, can use elementary 

 sulphur as a hylogenic food. 



Tlie Halogens, chlorine, bromine, iodine, and fluorine, are 

 elements which are closely similar in their chemical reactions 



