327 



STRANGE DEVELOPMENTS OF STOMATA ON CARYA ALBA CAUSED 



BY PHYLLOXERA.* 



By D. A. OwEX, I'Vanklin, Ind. 



The stoinata or breathing pores of Garya alba are naturally all devel- 

 oped upon the lower epidermis of the leaf. But, owing to the oviposit- 

 ing of the Phylloxera in the leaf through the lower epidermis, there is 

 developed upon the upper side a hemispherical gall. This gall, like all 

 other galls, is the nest of the insects, and in due time the young of the 

 Phylloxera may be seen issuing from a slit upon the lower side of the 

 leaf. 



Upon the lower epidermis, beneath the gall, may be seen a changed 

 form of cell structure in which there are to be found in almost every case 

 no stomata. But upon the upper side of the gall there are stomata in- 

 variably found, but not in as great abundance as are found upon the 

 lower epidermis of a normal leaf. 



In and around the opening of the gall there are to be found numerous 

 single-celled hairs, all of which j)oint outwards, as if guarding the ovum 

 and young from the ravages of an enemy. 



That which remains yet to be solved is : For what purpose are these 

 stomata developed upon the upper side of the gall ! Does the plant 

 develop these trichomes for its own use, or for the protection of the in- 

 sect ? Is the insect injurious or beneficial to the plant! 



It is hoped future investigations will solve some of these problems. 



EXTRACTS FROM CORRESPONDENCE. 



Destruction of Plant-lice in the Egg State. 



Do you think it practicable to destroy the eggs of the Aphis by spraying any sub- 

 stance on the tree or shrub during the latter part of the winter? I have tried kero- 

 sene in various strengths up to 30 per ceut, and it does not do the work. I have been 

 experimenting in the hope of finding something that will dissolve the shell of the 

 egg, but find it extremely resistant, scarcely yielding to the strongest acids and alka- 

 lies. I have been advised to try some of the; fixatives that entomologists use for 

 staining chitine, but nothing that I have tried appears to penetrate the shell at all, 

 so far as I can determine witli the microscoi)e. Please tell me if any experiments 

 have been made in this line, and if you would advise me to continue my investiga- 

 tions.— [E. S. Golf, Wisconsin, March 10, 1892. 



Eeply. — I do not think that you will find any substance that will destroy the egg 

 of j)lant-lice as eft'ectually as will the kerosene emulsion. I think it more thau prob- 

 able that you will find that the eggs which you have treated, though they may show 

 signs of life, will not liatch. My past experience would indicate that the eggs of 

 plant-lice when thoroughly sprayed with kerosene-soap emulsion did not hatch, and 



* Read before the Indiana Academy of Sciences, December 30, 1891. 



