120 



ANATOMY. 



which contains it. Starch-grains may be easily examined by moistening a slice 

 of cellular tissue containing them ; a drop of iodine will then jpolour the starch- 

 grains blue- violet, and bring out clearly the distinction between the cell and its con- 

 tents. If there be grains of albumen accompanying the starch-grains, the iodine 

 will colour them brown or yellow. 



Chlorophyll or chromule is a green substance, which forms flakes of a gelatinous 

 consistence floating in the colourless liquid of the cells ; these flakes have a tendency 

 to gather around or collect on the inner cell-walls, or on the contained starch or 

 aleurone grains. Chlorophyll constitutes the green colour of plants ; it is dissolved 

 by alcohol, whence it has been supposed to be of a resinous nature. 



The yellow colouring matter of cells is similar in consistence and properties to 

 chlorophyll ; but red, violet, or blue colouring matters are always liquid. 



Aleurone abounds in ripe seeds, and is always found either in the embryo or 

 albumen. Hartig considers an aleurone grain to be a vesicle with a double 

 membrane, containing a colourless waxy mass, which is coloured yellow by iodine, 



and is ordinarily soluble in water. 

 In certain plants it assumes a 

 well-defined crystalline form (figs. 

 674, 675) ; in others, the nucleus 

 of the aleurone mass has crystal- 

 lized, while the surrounding layers 

 remain amorphous, and thus the 

 grain presents a round or ovoid 

 form. Aleurone is essentially 







formed of substances which are 

 collectively termed protein (for 

 which see the section on Vegetable Physiology). 

 According to Hartig, the particles of the nucleus 

 undergo the following transformations : 1, the nucleus 

 is transformed directly into chlorophyll, fecula, or aleurone ; 2, it is transformed 

 into starch and the starch into aleurone ; 3, it is transformed into chlorophyll, 

 and that into starch, which again passes into aleurone. 



The laticiferous vessels contain a large quantity of powdery granules, which 

 float in the latex, some of which are very large and colourless, and partake of the 

 nature of starch. 



As to the sap which fills these cells, and rises in the vessels, it is a colourless 

 liquid, holding in solution the materials for cell-formation and cell-contents. The 

 other liquids, either contained in the cells, or in the intercellular spaces, are fixed or 

 volatile oils, turpentines, sugar or gum, dissolved in water. Finally, we find gases 

 occupying the intercellular spaces, sometimes at considerable depths. 



Besides the solid organic substances above described as occurring in the 

 cellular tissue, special cells occur, containing mineral substances, the elements of 

 which, either compound or simple, have been carried up by the sap, and have cry- 

 stallized in the cells. Those of which the elements were originally in combination 



674. l.;it lirii :l. 



Cell containing crystals of 

 aleurone, in the midst 

 of cells containing chlo- 

 rophyll. 



673. Rumcx. 



Cells containing 



raphides. 



