56 BOTANY. 



bodies contain an additional blue pigment. It is present in many 

 plants which are destitute of chlorophyll ; this is the case with the 

 parasitic Phanerogams ; it occurs, for example, in the stem of Cuscula, 

 and in the underground portions of Orobanche and Lathrcea. From 

 chlorophyll-less Thallophytes (fungi), with rare exceptions, it appears to 

 be absent.* 



(6) The best common examples for the study of fully formed starch 

 grains are the following, viz., tubers of the potato, seeds of the bean 

 and pea, grains of wheat, Indian corn, rice, etc. Oat-starch and that 

 of the crocus corm exist in the form of compound grains. Of those 

 named, the starch grains of the potato and the bean are the largest, 

 being about .07 mm. (.003 inches) in diameter, while those of rice are 

 the smallest, being about .007 mm. (.0003 inches) in diameter. 



(c) The test which is characteristic of starch is its blue coloration when 

 treated with a weak solution of iodine. When the solution is strong 

 the color is so intense as to appear black. A careful examination shows 

 that it is only the gran ulose which is thus colored blue by iodine, 

 but on account of its much greater quantity and its intimate mixture 

 with the starch-cellulose, the blue granulose gives its color to the 

 whole grain. 



(d) An indication of the correctness of the present view as to the 

 structure of the starch grain and the cause of stratification may be 

 obtained in two ways, as follows: 1st, by thoroughly drying the grain 

 by evaporation of its water or by placing it in absolute alcohol ; all 

 parts having now equal amounts of water, the striae disappear ; 2d, by 

 rendering all parts of the grain capable of absorbing large quantities 

 of water, as may be done by means of a weak solution of potash, as in 

 this way the difference in the amount of water in different layers 

 being destroyed, the striae disappear as before. 



The drying process just referred to reveals another structural pecu- 

 liarity, viz., that the interior portions of the starch grain contain the 

 greatest amount of water. On drying, internal fissures appear, radiating 

 from a central cavity and having a narrower diameter as they pass out- 

 ward, showing that the loss of water is greatest in the interior. 



(e) The separation of the granulose from the starch-cellulose may be 

 accomplished in the following ways : (1) by allowing the starch grains to 

 remain for a long time in a weak solution of hydrochloric or sulphuric 

 acid ; the acid solution must not be strong enough to cause the grains 

 to swell ; (2) by the action of saliva at a temperature of 40 to 47 C. 

 (105 to 117 Fahr.). In either case the granulose is removed and the 

 starch cellulose remains as a skeleton. Upon treatment with a solu- 

 tion of iodine the skeleton is colored brown instead of blue. Other 



* Hofmeister, in " Lehre von der Pflanzenzelle," from which the 

 preceding statements have been mainly taken, states that starch gran- 

 ules occur in the oospores of Saprolegnice. 



