19 



myct'liiil-liko stnictiuc hclicvod to be left by the aphis wtis always 

 presiMit, extending" from the surfaee of the leaf down to the soft bast of 

 the vascular bundle, and often l)eyond into the central niesophyll por- 

 tions of the leaf (tij^s. 2 and o, and PI. 11, lig. 4). Large numbers of 

 cultures were also made from spots known to be produced by aphides, 

 but with the same negative results as before described. 



Similar experiments with thrips showed conclusively that they are 

 the cause of the elongated spots (tig. -4, and Pis. 1 and 111) and the dis- 

 tortion of the foliage, and it was also found that the red spiders work- 

 ing on the immature leaves produced the very minute spots by sucking 

 th(» nourishment from the epidermal cells and those immediately 

 underlying. 



Fig. 4.— Cross section through a fully developed spot produced by thrips. The epidermal cells have 

 collapsed and the underlying palisade parenchymal cells are somewhat elongated and have lost 

 most of their chloroplasts. (Drawn with Zeiss camera lucida, x 282 diameters.) 



It was thought desirable to get more accurate information in regard 

 to the manner in which aphides obtain their nourishment from the 

 tissues, and for this purpose leaves upon which they had been col- 

 onized .were carefully cut from the plant while their sucking apparatus 

 was still inserted in the tissues. These leaves were dropped into 75 per 

 cent alcohol saturated with corrosive sublimate, and many of the aphides 

 were thus killed before they had time to withdraw their beaks or punc- 

 turing bristles. Portions of the leaf with the beaks attached were 

 then cut out, carefully dehydrated, and infiltrated with parafiin, the 

 sections being then cut and mounted in series, and thus preparations 

 showing the puncturing apps^-^+us in place in the tissues obtained 

 (fig. 5, and PL II, figs. 2 and 3^. Tbe- puncturing bristles always 



