The Effect of Borax in Fertilizers. Ill 



■shoot formed in its axil would appear entirely healthy at the 

 same time. However these leaves from the younger shoots 

 nearer the base later showed the same marginal injury. 



The dead tissues suggested more of an olive tinge than a 

 browning. A comparison with standard color charts failed to 

 match any shade or tint of brown except possibly in the case of 

 the first appearance of the injury on the tip of a leaflet. The 

 color was difficult to match and about the best description that 

 can be given is that it resembled most closely what might be ex- 

 pected where a potato leaf had been killed rapidly and quickly 

 dried with little yellowing. 



The appearance of the affected leaves seemed to indicate 

 simply a progressive death and drying out of the tissues. While 

 there was a fairly sharp line of demarkation between the 

 diseased and healthy portions of the leaves, the latter near this 

 line usually showed more or less fading out of the normal green 

 color to a lighter green or even a yellowish tinge. In advanced 

 stages the leaf-blades themselves would become yellow, soon fol- 

 lowed by the dropping of the leaf. Some of the more severely 

 injured plants lost all of their leaves before they were dug up 

 early in January. 



In some instances there was a suggestion of what has been 

 called "tip-burn" of the potato. However, there is no reason for 

 confusing this tip and marginal injury on greenhouse plants, 

 resulting from borax applied to the soil with the fertilizer, with 

 the usual forms of the tip-burn in the field. It occurred under 

 relatively humid conditions, at a time of the year when sunlight 

 was at its lowest intensity, and in greater degree on the plants 

 supplied with an abundance of moisture. The plants were en- 

 tirely free from insects of all kinds. 



Several facts, taken together, strongly suggest that this tip 

 and marginal injury is the direct result of the accumulation of 

 compounds of boron in the tissues affected. Droplets of liquid 

 were constantly observed upon the tips and margins of the 

 leaflets of potato plants grown in the greenhouse particularly 

 at the times when no other explanation could be given for their 

 presence, except that they exuded from the leaves themselves. 

 Moreover faint traces of a whitish deposit were repeatedly 

 seen on these leaves in the same locations after the droplets had 

 evaporated. This condition was found to be common and was 



