22 ORGANOGRAPHY. 



violet, the disting^uishing character of starch and some othermat- 

 ters closely allied to it, as cellulose and amyloid; which latter 

 is a substance found occasionally in the secondary deposits in the 

 albumen of some seeds. Tlie blue color is at once destroyed 

 by the application of heat and alkalies. If starch be exposed 

 to heat for a prolonged period, it is converted into a soluble 

 gummy substance, called dextrine or British gum. A similar 

 change is produced in starch by the action of diluted sulphuric 

 acid, and diastase, a peculiar nitrogenous substance occurring 

 in germinating seeds. Starch was formerly considered as pecu- 

 liar to plants, and its presence therefore Avas regarded as an 

 absolute distinctive mark betAveen them and animals. Of late 

 years however, a substance presenting the chemical reactions 

 and general appearance of starch has been found in some 

 animal tissues. Such a distinctive character, therefoi'e, can 

 be no longer absolutely depended upon. 



Starch has been described as occurring in two states, either 

 in an amorphous condition, or in the form of distinctly defined 

 granules. Its existence in an amorphous state has been de- 

 scribed by Schleiden as found in the bark of the Jamaica Sarsa- 

 parilla, in the seeds of Cardamomum minus, and in the under- 

 ground stem of Carex arenaria. The existence of starch in 

 this amorphous condition is, however, by no means clearly 

 ascertained. Starcli commonly occurs in the form of colourless- 

 transparent gi'anules, varying in size ; which are either distinct 

 from each other as is generally the case (Ji'j. 36), or mora 

 or less combined so as to form compound granules (Jig. 41). 

 "When fully formed it is usually found floating in the cell-sap, 

 but in a young state it is attached at one point of its surface 

 to the protoplasm or primordial utricle, from which struc- 

 tures, as will be presently seen, it is believed to be developed. 

 In form the granules are always spherical or nearly so in 

 their earliest condition. In some cases this form is nearly 

 maintained in their mature state, as in wheat starch (Jig. 42); 

 but they frequently assume other forms, as ovate, elliptical, 

 more or less irregular, club-shaped, or angular (see figures). 

 Such arise from the unequal dcvclopmciit of the sides of 

 the granules, or Irom mutual pressure, the same causes indeed 

 which give rise in a great measure to the varying forms of the 

 cells in which they are contained. Starch granules vary also 

 extremely in size in different plants, and even in the same cell. 

 The largest granules known a])pear to be those of the Potato 

 (Jig. 40). and Canna starch, or, as it is commonly termed, "Tous- 

 les-mois," where they are sometimes as nuicli as the --tn of an 

 inch in length (Jig. .39) ; while the smallest granules, among 

 which may be mentioned those of liice starch (Jig. 43), are 

 sometimes too snnill to be accurately measured, being fre- 

 quently under ^^ of an inch in length. 



