758 



SCIENCE 



[N. S. Vol. XLIV. No. 1143 



P. S. As this goes to press, November 17, 

 nine of the thyroidless tadpoles are still alive 

 and have increased in size. One has been fed 

 thyroid preparations for 25 days but in very 

 small amounts and at long intervals for fear 

 of fatal results. The hind legs have reached 

 a length of 9.5 mm. and the fore legs are evi- 

 dent beneath the skin. The tail has become 

 greatly shortened and the head is assuming 

 the character of a frog's head. The legs of all 

 the other tadpoles have remained stationary 

 in development at a length of 4 mm. and the 

 tadpoles as a whole show no further signs of 

 metamorphosis. Another tadpole of 29 mm. 

 heavily fed with thyroid, died after 4 days. 

 When compared with a thyroidless tadpole of 

 practically equal body length it was found the 

 intestine of the thyroid fed tadpole had been 

 reduced to a length of 143 mm. as compared 

 with 237 mm., the length of the intestine of 

 the thyroidless tadpole that had not been fed 

 thyroid. B. M. A. 



MICROTECHNICAL METHODS FOR STUDYING 



CERTAIN PLANT-SUCKING INSECTS 



IN SITU 



A problem on which the writer has been 

 working for the past year, viz., determining 

 the relation of certain sucking insects to their 

 host plants, has necessitated the development 

 or adaptation of several points of microtech- 

 nique which may be of use to other investiga- 

 tors along similar lines. Sectioning insect 

 and plant tissue together has not been at- 

 tempted often, as the usual methods suitable 

 for one are out of question for the other. It 

 is also necessary to cut quite hard tissues and 

 to employ stains for chitin which also will not 

 dissolve the middle lamellae separating the 

 plant cell-walls. 



The material for study must be fresh. 

 Usually most satisfactory results are obtained 

 if the bottles of killing fluid are taken into 

 the field, the parts of plants bearing the in- 

 sects cut off with a sharp knife, and immedi- 

 ately immersed. Aphididse and others of the 

 more active forms must be removed with the 

 part of the plant on which they are feeding 

 and killed before they have time to pull out the 

 proboscis, otherwise their natural positions in 



feeding can not be studied. For the gelatine 

 method of embedding, which the writer has 

 used quite extensively, pieces of pine needles, 

 each bearing a coccid at one end, are tied in 

 bundles of ten to twenty, making it possible to 

 get sections of many needles at once; with the 

 use of a killing and fixing agent which pene- 

 trates rapidly and easily no difficulty from im- 

 proper fixing of parts of these bundles is ex- 

 perienced. 



Of the killing solutions a variety was tried, 

 JeffryV proving in most cases the most satis- 

 factory, as the picric acid in it stains chitin. 

 Also it softens hard plant tissues so that it is 

 possible to cut paraffin sections of leaves as 

 hard as Citrus without further softening. It 

 may be used hot for twenty minutes or cold 

 for several hours. Care must be taken to wash 

 thoroughly in alcohol or iodin alcohol (30 per 

 cent, alcohol which has been turned to a light 

 wine color by the addition of iodin), otherwise 

 crystals of mecuric bichlorid will remain. 

 Carnoy's fluid- 2 also proves successful, partic- 

 ularly with active insects having much secre- 

 tion of wax, e. g.j the aphid Chermes, which 

 with less quickly penetrating solutions en- 

 closes a drop of air, thus enabling the insect 

 to free its beak before death. Its hardening 

 properties are overcome by thorough washing 

 in absolute alcohol, followed by 95 per cent., 

 85 per cent., 70 per cent., 50 per cent., 30 per 

 cent, strengths, and then softening in Jeffry's 

 solution. 



The gelatine method for embedding 3 has 

 been found by the writer very successful for 

 many hard tissues. It deserves extended trial 

 with plant tissues usually considered too hard 

 for sectioning. It is a short method: the ma- 

 terial does not require dehydration before its 

 use, therefore hard tissues are not rendered 

 harder than they naturally are. Further, the 



i Corrosive sublimate, saturated solution in 30 

 per cent, alcohol, 3 parts. Picric acid, saturated 

 solution in 30 per cent, alcohol, 1 part. 



2 Absolute alcohol 6 parts, chloroform 3 parts, 

 glacial acetic acid 1 part. 



3 Land, W. J. G., ' ' Microtechnical Methods, ' ' 

 Bot. Gas., Vol. 59, May, 1915, p. 400. Chamber- 

 lain, C. J., "Methods in Plant Histology," 3d re- 

 vised edition, p. 128. 



