88 LON A. HAWKINS 



In the order of their toxicity, Pb(NO 3 ) 2 follows the copper salts, though 

 not closely, with A1(XO 3 ) 3 next. The effects of the last two salts on 

 plants seems to have been studied but little. Livingston [05] employed 

 them, however, and found the same relation to hold true as is here brought 

 out. Also, Jensen [07] found that Pb(NO 3 ) 2 is somewhat less toxic toward 

 wheat seedlings than is Cu(NO 3 ) 2 . The nitrates of zinc and nickel, which 

 are next in the order of diminishing toxicity, are not exceedingly toxic 

 toward these Gloeosporium spores. It is interesting to note that Clark [99], 

 working with fungi, and Livingston [05], with an alga, found nickel salts 

 to be more strongly toxic than those of zinc, results which are opposite 

 to those obtained in this investigation. 



Magnesium, calcium, and potassium nitrates and cane sugar end the list, 

 in the order named. It is noticeable that, with these last four compounds 

 at concentrations just below that required to inhibit germination, growth 

 takes the form of swollen bodies which tend to give a lower value to the 

 ratio of surface to volume of the organism than that resulting from normal 

 germination. This reaction to toxic stimuli, at concentrations just below 

 those required to inhibit growth, occurs commonly with all the salts here 

 used. That it is found with cane sugar, which is usually regarded as 

 non-toxic (see True 27 ) suggests that such reactions may be brought about 

 by high osmotic pressure as well as by chemical stimulation in the true 

 sense of this term. This suggestion is in accord with the conclusions of 

 Livingston [05], who has shown that his form of Stigeoclonium assumes 

 the palmella form in response either to a chemical stimulus or to one of 

 relatively high osmotic pressure. Whether this effect of sugar, and similar 

 effects produced by high concentrations of calcium, magnesium and 

 potassium nitrates is really due, in the present instances, to osmotic pressure 

 relations, was not determined experimentally ; the minuteness of the spores 

 must render experiments involving plasmolysis exceedingly difficult with 

 such organisms as those here employed. It is obvious, however, that, the 

 high concentrations of the calcium, magnesium and potassium salts, found 

 necessary to affect germination, must be capable of exerting an extremely 

 high osmotic pressure if the ectoplasm of the spore is not readily permeable 

 to them. 



From table IV it may be seen that, with the exception of HNO 3 , the dif- 

 ferent compounds arrange themselves in the same order no matter what 

 type of reaction to the chemical stimuli may be taken as criterion. This 

 suggests that the physiological response of death, on the one hand, and 

 the various morphogenic responses considered in this paper, on the other, 

 are ultimately related to the same properties or characteristics of the various 



27 True, Rodney H., The physiological effects of certain plasmolyzing agents. Bot. Gaz. 26: 407- 

 416. 1898. 



