PLANT LIFE. 



are characteristic of special changes which the wall may- 

 undergo. The most noticeable changes are four: (i) Some 

 cell-walls contain suberin or cutin, fat -like substances by the 

 presence of which water and gases are hindered from passing 



I 1 



\ 



Fig. 8. 



Fig. 9. 



Fig. 8. — I, chromoplasts from flower-leaves of an orchid; II, from the root of carrot; 

 III, from the fruit of mountain-ash. Embedded in the protoplasmic body of the 

 chromoplast are sometimes proteid crystalloids,/, pigment-crystals, /, or starch- 

 grains, s. Magnified about iooo diam. — After Schimper. 



Fig. 9. — Chromoplasts from the flesh-colored shoots of the horsetail, containing the 

 coloring matter in the form of granules embedded in colorless protoplasm. Mag- 

 nified 1400 diam. — After Zimmermann. 



through. The cell-walls of bottle-cork are suberized, and 

 those in the skin of the apple are cutinized. (2) Some cell- 

 walls are lignified, as, for example, those of wood by reason of 



Fig. 10.— A part of a thin slice lengthwise through the centre of the stem of garden- 

 balsam. The cells and vessels are elongated and are here seen from the side, show- 

 ing the thickened lines on the side walls of v y v', v", v"', v"", and v'"". Mag- 

 nified about 400 diam. — After Duchartre. 



the presence of certain substances (vanillin, coniferin, etc.). 

 They allow the ready passage of water and gases. (3) Others 

 are so transformed that, in contact with water, they swell 

 enormously, forming a mucilage or gum. These swelling 



