72 THE NORTHERN MICROSCOPIST. 

as starch, and stored up as a reserve food material, being found in large quanti- 
ties in bulbs, tubers, seeds, pollen grains, and in those organs which, when 
vegetation awakes, are the starting points for the new formation of cells. On 
the recommencement of growth or germination, the starch is reconverted into 
dextrine or sugar, is then soluble in water and becomes absorbed by the proto- 
plasmic contents. This change is necessary before it can afford nourishment to 
the growing parts of plants. Its composition is also altered by the addition of 
three parts of Hydrogen, being now Carbon, 6 ; Hydrogen, 13 ; Oxygen, 5. 
Under ordinary conditions the granules are insoluble in cold water, but swell 
up very strongly in boiling water. They are readily detected by means ofa 
solution of Iodine, which colours the granules a dark blue or purple. No other 
substance but starch has this distinctive blue appearance under the influence 
of Iodine. 
With the polariscope the granules become coloured in a peculiar and beauti- 
ful manner, revealing the characteristic black cross, which, according to Ganot 
and Deschanel, is due to the power of double refraction, a property possessed 
by many other organic substances. The cross takes the form of four arms 
meeting together at the hilum, and which onrevolving the polarizer, are alternately 
black or white, with an intermediate shade of cross exactly between the two 
extremes. The largest granules known are those from the Canna édulis, popu- 
larly known as Tous-les-mois, a plant similar in characteristics to the Arrowroot, 
its average.size in thousandths of an inch being 3°5 x 2°3, while the smallest 
are from the Parsnip, and only measure i045 oo Of an inch in diameter, being 
so minute as to require high magnifying power, and only recognizable with 
difficulty. 
A variety of starch obtained from the tubers of Dahlia, Jerusalem Artichoke, 
and a few other plants is termed Inuline, and Lichenine is the peculiar starch 
of Lichens, and is found in Iceland Moss, Reindeer Moss, and Carrageen, or 
Irish Moss. 
Starches should be mounted in carbolized water for ordinary refracted light, 
and in balsam or dammar for polarizing. 

To the beginner, no other objects present so few difficulties, the material » 
being almost ready to his hand. For carbolized water one ring of cement is 
sufficient, with another for fixing the cover, and one or two drops of carbolic 
acid is enough for any reasonable quantity of water. By placing a small quan- 
tity of the starch in the centre of the slide and just tapping the slide with your 
finger or thumb, a sufficient layer of starch will adhere ; the rest of which can 
be blown off. For mounting in balsam or dammar, centre the cover glass of 
the thin layer of granules, when two drops of the media placed at two sides of 
the cover, but not exactly opposite, will, by capillary attraction, permeate the 
whole of the space under the cover glass, without displacing the starch, and can 
then be put away to harden and ring in the usual manner.” 
During the conversation which followed, the undermentioned objects were 
shown :— 
Dar var or crane=ty vt) seccsct. ke. ety ees ereea eet ere Mr. H. Hall. 
Head of caterpillar, mounted without pressure............ +3 
Mature polypite of Zbularia larynx....ccecrevsenes Mr. H. Chadwick. 
Pleurosig nia ANQUlatusnt ..cciciscscvcevevecencvevscceees vevees Mr. D. Alston. 
Starchesin Gum Damar .............descsssesseseceert ene Mr. E. Napper. 
55 @arbolizad Water”. ree eee rece eae Mr, W. Stanley. 
Oil immersion condenser and diatoms............-..++++5 Mr. E. Napper. 
Trichodactylus osmia (bee Mite) .......cseeseeeeeeee wae 
UOOSSEP TR STRUOSE NIMles eae te TEU Tee ae overeat eee Mr. Alex, Hay. 
VA CCEMOCYCLUS TRAUSUL A Weeden eients Vhs de Weotued 
Section of potato (showing starch 272 S722) ..ssseseeeeseeeee eens Mr. Miles. 
IN yinply Of GoMseR eA Porch aT es eels eet Mr. W. Blackburn. 
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