48 



BOTANICAL GAZETTE 



[JANUARY 



0.005 ^j b^^ ^^ o.ooi m root hairs were developed, and in o.oooi nt 

 branches were sent out similar to those in CaCl^ solutions. 



The following table gives the average length of roots per plant 

 produced in the various solutions, the figures being based on seven 

 duplicate series of experiments. 



Salts 



Concentrations 



0,02 m 



0.04 m 



MgCl. 

 NaCl. . 

 KCi... 



CaCla. 



446 



462 



321 



333 

 386 



0,06 m 



o.oS m 



IS 



mm 



220 



lOmm 



134 



144 



168 



0.12 m 



Q.iSm 



^min 



54 



63 



84 



Qinin 



24 



31 

 48 



Distilled water, 740"^™ 



These results are also shown in fig, i in the form of curves, the 

 concentrations being used as ordinates and the average length of 

 the roots per plant being used as abscissae. The cur\^es show that 

 little growth took place at o. 18 m in sodium, potassium, and calcium 

 chlorids, and none whatever in magnesium chlorid. The small 

 growth in magnesium chlorid throughout the whole series of con- 

 centrations is due mostly to its toxic action; but also in some degree 

 to its higher osmotic pressure. The molecule of MgCl^ when dis- 

 solved dissociates into three ions instead of two, as in the case of 

 NaCl and KCI; hence MgCl, solutions have a higher osmotic pres- 

 sure than equimolecular solutions of NaCl and KCI. 



^ All the more striking is the beha\ior of CaCl^ which in spite of 

 high osmotic pressure (approximately as high as IMgCl,) nevertheless 

 permits greater growth than NaCl or KCI; hence it must be much 

 less toxic than any of the other salts. 



RESULTS 



1. Each of the principal soil bases (Na, K, Mg, Ca) is toxic. The 

 following is the order of toxicitv of their chlorids: (i) INfgCl,, 

 (2) NaCl, (3) KCI, and (4) CaCl,. 



2. Experiments lasting but a short time (such as have been made 

 by most pre\ious investigators of the toxic action of salts) cannot 

 be considered as conclusive as longer experiments. After six days, 



