424 THE MICROSCOPE. 



as shown in fig. 202, and Plate XVI. from the garden rhubarb. Starch- 

 grains are variable in size : the tous-les-mois, No. 5, are very large ; 

 in the potato, No. 14, they are smaller; and in rice, No. 6, they are very 

 small indeed. Nearly all present the appearance of concentric irre- 

 gular circles ; and most of the granules have a circular spot termed the 

 hilum, around which a large number of curved lines are arranged : seen 

 best by polarised light. 



Leeuwenhoek, to whom we are indebted for the earliest notice of 

 starch-granules, enters with considerable minuteness into a description 

 of those of several plants such as wheat, barley, rye, oats, peas, beans, 

 kidney-beans, buckwheat, maize, and rice ; and very distinctly describes 

 experiments made by him in order to investigate the structure of their 

 starch-granules. Dr. Reissek regards the granule as a perfect cell, from 

 the phenomena presented during its decay or dissolution, when left for 

 some time in water. Schleiden and others, after examining its expan- 

 sion and alteration under the influence of heat and of sulphuric acid, 

 considered it to be of a solid homogeneous structure. 



Mr. Busk, after devoting considerable attention to the subject, 

 agrees with M. Martin in believing the primary form of the starch- 

 granule to be " a spherical or ovate vesicle, the appearance of which 

 under the microscope, when submitted to the action of strong sulphuric 

 acid, conveys the idea of an unfolding of plaits or rugae, which have, as 

 it were, been tucked in towards the centre of the starch-grain."* The 

 mode of applying the concentrated sulphuric acid is thus described by 

 Mr. Busk : " A small quantity of the starch to be examined is placed 

 upon a slip of glass, and covered with five or six drops of water, in 

 which it is well stirred about ; then with the point of a slender glass- 

 rod the smallest possible quantity of solution of iodine is applied, which 

 requires to be quickly and well mixed with the starch and water ; as 

 much of the latter as will must be allowed to drain off, leaving the 

 moistened starch behind, or a portion of it may be removed by an in- 

 clination of the glass, before it is covered with a piece of thin glass. 

 The object must be placed on the field of the microscope, and the ^-inch 

 object-glass brought to a focus close to the upper edge of the thin 

 glass. With a slender glass-rod a small drop of strong sulphuric acid 

 must be carefully placed immediately upon, or rather above the edge 

 of the cover, great care being necessary to prevent its running over. 

 The acid quickly insinuates itself between the glasses, and its course 

 may be traced by the rapid change in the appearance of the starch- 



* G. Busk, F.R.S., on the Structure of the Starch-granule; Quarterly Journal of 

 Microscopical Science, April 1853. 



