HARDWICKE'S SCIENCE-GOSSIP. 



255 



its adoption, the United States, from which large 



quantities packed in barrels and preserved in tins are 



sent to England every year. Some years so plentiful 



is the crop in many parts, that it has become a practice 



to employ the surplus of sweet apples in fattening 



pigs, &c. Perhaps one of the most delicious of the 



dessert apples which stands at the head of the list of 



American-grown fruit is the Newtown pippin, and 



which certainly fetches a higher value in Covent 



Garden market than any other kind. One of the 



finest orchards in the New World on the banks of the 



Hudson contains more than 2000 of these trees. The 



Siberian crab apple was not cultivated in Britain until 



1758, and the small fruited variety was introduced in 



1 7S4 ; this tree is often planted as an ornament in our 



shrubberies. 



( To be continued.) 



MICROSCOPY. 



How to Remove Air-Bubbles. — Air-bubbles, 

 whether in balsam, glycerine jelly, or fluid mounts, 

 are a constant source of annoyance to the amateur 

 mounter. I will endeavour to show how these pests 

 can be avoided. Firstly, with respect to balsam. 

 Mr. Stokes, some months since, gave a plan which 

 will answer in very many instances ; but there are 

 objects which will not stand the boiling recom- 

 mended by Mr. Stokes, in such case the air can be 

 got rid of by immersing the object in boiled water 

 still lukewarm, and changing the water every two or 

 three hours until the air is wholly displaced (boiled 

 water absorbs air most greedily). The object is 

 then transferred from the water into alcohol, absolute 

 alcohol and oil of cloves in succession, allowing it 

 to remain a sufficient time in each to displace the 

 water or other fluid ; the object can be mounted in 

 balsam direct from the oil of cloves. The difficulty 

 with glycerine jelly is that it begins to thicken imme- 

 diately it is put on a cold slide, and when the cover 

 is put on, air-bubbles are almost sure to be enclosed. 

 The way to obviate this difficulty is to have the glass 

 slip lying upon something heated to 150 or there- 

 abouts, such as a hot-water plate or block of iron 

 taken out of an oven ; by these means the jelly is 

 kept fluid whilst the object is being mounted ; the 

 cover must be breathed upon on its under surface 

 previously to being lowered in its place ; as soon as 

 this is done the slide can be removed from the heated 

 plate or iron, and the jelly allowed to set. It merely 

 requires ordinary dexterity to mount an object in 

 fluid in accordance with instructions given in works 

 on this subject, but it certainly is an annoyance to 

 an amateur mounter to find bubbles making their 

 appearance when he knows that none were to be 

 seen when the object was first mounted, and that the 

 cement was good and reliable and properly applied. 

 The question naturally arises, where do the air- 



bubbles come from ? I have seen this attempted 

 to be accounted for in several ways, but not to my 

 satisfaction. The true explanation is that the pre- 

 servative fluid itself contains "free" air; expel the 

 air before using the fluid, and no bubbles will after- 

 wards make their appearance providing the other 

 part of the mounting be properly carried out. To 

 expel the air from the preservative fluid, all that is 

 necessary is first to fill the cell well with fluid and 

 to place the slip upon a hot-water plate or heated 

 iron ; minute bubbles will shortly appear and can be 

 detached from the bottom and sides of the cell by 

 means of a bristle ; they will collect at the top of 

 the fluid and can be removed by just touching it with 

 a little blotting paper ; the slide must then be taken 

 off the heated surface, the object immersed in the 

 fluid and the cover put on and fastened in the 

 ordinary way. If all be done properly no bubbles 

 will afterwards be seen ; on the contrary, I have at 

 times actually enclosed a little air by accident when 

 putting on the cover, which air has afterwards been 

 absorbed by the fluid. — H. M. 



Staining Fluids for Vegetable Tissues. — 

 For some time past I have thought it rather "hard 

 lines" upon the microscopical botanists that but one 

 staining fluid has been used at a time. I have, there- 

 fore, tried several experiments with different fluids, 

 and I am glad to say I have at last found out a most 

 successful method of staining one section with two 

 fluids. The way I now stain all my sections prepara- 

 tory to mounting them is this : the section is first 

 immersed in an aqueous solution of Crawshaw's 

 aniline blue dye (strength, 1 per cent.). It is then 

 removed into strong acetic acid, which seems to 

 fix the colour in certain tissues, remove it from 

 others and prepare that not stained for the reception 

 of another colouring fluid. It is then again removed 

 and put into a weak solution of magenta (Judson's 

 dye), also made strong with acetic acid ; then 

 mounted in glycerine jelly. I find this such a beau- 

 tiful and instructive method of staining (as it com- 

 pletely shows the " differentiation " of parts, both by 

 the different colours and also the various intensity 

 of colour) that I venture to ask room in your paper 

 for its insertion, in order that others may be made 

 acquainted with a system so simple, yet, which has 

 cost me much trouble and many failures. The 

 following are the colours with which the tissues of 

 a section of Burdock are stained : — ■ 



Pith Very pale magenta. 



Cellular tissue Deep magenta. 



Spiral vessels of medullary sheath Deep blue. 



Pitted vessels Blue. 



Cambium Deep blue. 



Liber cells Dark magenta. 



Latiferous vessels Deep blue. 



Cuticle parenchyma .... Pale blue. 



Epidermis Deep blue. 



Hairs Pale magenta. 



— Albert Henry Barrett. 



How to Restore Microphotographs. — In 

 reply to Mr. H. Heasman's inquiry I beg to inform 



