118 PLANT ANATOMY. 
of their stratified structure, are also doubly refractive. In pola- 
rized light each granule displays a black cross, the arms of 
‘ which intersect at the hilum (Fig. 52). 
When the structure of the granule is destroyed, either through 
tumefaction or by torrefaction, it immediately loses its optical 
properties, though agents which produce swelling, but which 
have neither an acid nor an alkaline reaction, produce no 
change, at least ina chemical sense, in the substance of the 
starch. The optical properties therefore appear to be dependent 
upon the manner of construction of the granule. Nevertheless, 
Nigeli entertains the view that the micelle’ of starch (a term 
which he applies to the complex of atoms, surrounded by a film 
of water, which through intussusception become separated from 
each other), like those of the denser cell-membranes, are origi- 
_ nally crystalline, and show the deportment of optically uniaxial | 
crystals, but only so long as they have not become disintegrated, 
which Nigeli assumes to take place upon swelling. 
Starch, as the most important reserve nutritive substance, is 
contained in an extraordinarily large number of reserve recepta- 
cles, thus in seeds (endosperm of the cereals, the cotyledons of 
many Leguminose), Semen Cacao, Sem. Myristice, Sem. Para- 
disi, Sem. Piperis (v. Piper album), Sem. Quercus, while Sem. 
Cydonia, Sem. Lini, Sem. Sinapis albe and probably others 
contain starch, at least before ripening. Furthermore, in rhi- 
zomes (Maranta, the Zingiberacexw, Aspidium Filiz-mas, Asa- 
rum, Calamus), in roots (Althea, Sarsaparilla, Krameria, Ipe- 
cacuanha, Rhubarb, Belladonna), and in tubers (Potato, Salep, 
Jalap, Colchicum). 
A remarkable exception is presented by the roots and rhi- 
zomes of the Composite, which contain no starch, or only tran- 
sitorily, and then but extremely small amounts of it. It is fur- 
thermore wanting in Radix Gentiane, Rubie, Saponaria, 
Senege, and in the rhizome of Triticum repens, at least in the 
Stages of development which here come under consideration. 
In all these organs its place is supplied by other substances. 
 Unjustifiable diminutive of mica, a small crumb. 
