400 Vegetable Physiuhr/ii. 



converted into a thin jelly-like sac, still insoluble in water. Very 

 often the power of resistance is unequal at different parts of the 

 structure, and the granule is first of all " blown out" out into one 

 or more partial sacs or bulgings, which ultimately coalesce when 

 the whole expands. This appearance may be produced by 

 allowing sulphuric acid to run in upon the granules from one 

 side of the slider. Still more frequently the granule bursts 

 while swelling up into a sac (fig. 12, d), and then we not unfre- 

 quently find some of the internal substance extravasated in cloudy 

 patches, which are rendered visible by applying iodine to the 

 object. 



When the starch granules of the potato (or tons-Ies-mois) are 

 carefully heated on a dry slider of glass, and placed beneath the 

 microscope, they present one of two appearances, the difference 

 depending seemingly on their degree of dryness. They either 

 split up, or rather exfoliate, the concentric coats cracking and 

 peeling off one after another (fig. 12, h), or they become softened, 

 lose tlie streaks, turn brownish, and swell into globules present- 

 ing a large central cavity formed by the expansion of the air 

 contained in the original small point-like cavity (fig. 12, c). In 

 both cases the starch has undergone decomposition as well as 

 change of form ; it has now become soluble in water, having 

 been converted, in fact, into the gum-like substance called dex- 

 trine. The continued action of sulphuric acid, of boiling water, 

 of substances producing fermentation, <S:c., likewise converts 

 starcli-granules into dextrine or sugar ; and doubtless this con- 

 version leads to the solution of the starch of seeds, &c., during 

 germination. But in the processes of germination the solution 

 of the granules takes place without a previous swelling up into 

 starch-jelly, and the appearances vary in different plants. 



When the starch of a well-sprouted seed-potato is examined, 

 the large granules are found in various stages of diminution of 

 size by superficial solution, by no means coincident with the 

 concentric coats : the end containing the cavity persists longest 

 (fig. 12, e). The compound granules of oats fall apart in germi- 

 nation, and are then dissolved from without inward. The grains 

 of barley (as observed in malt) exhibit a different mode of solu- 

 tion ; holes are formed in the outer coat, and the solution gra- 

 dually eats out the contents, leaving a shell ; singularly enough 

 the same appearance occurs also in potato-starch when acted 

 upon by fermenting yeast. 



The mode of origin or development of the starch-granule has 

 formed a subject of considerable debate among vegetable physi- 

 ologists, but the principal facts may now be considered as ascer- 

 tained. From the laminated character of large grains of starch, 

 several observers were led to compare the starch-granule with 



