150 A TEXT-BOOK OF BOTANY. 



consisting of protein matter, and an outer layer, consisting of a 

 number of starch grains. The studies of Baubier tend to show 

 that the pyrenoid is perfectly differentiated and independent of 

 the chromatophore, and that the starch is formed from a leuco- 

 plastid which surrounds a phyto-globulin or crystalloid at the 

 center. This would quite agree with the studies of Timberlake, 

 who observed the complete conversion of the pyrenoid into starch. 

 That the substances of the pyrenoid are in the nature of reserve 

 food materials, is apparent from the fact that the pyrenoid entirely 

 disappears in Hydrodictyon prior to spore formation, and that 

 it is afterward formed anew in the young cells, thus behaving 

 very much like a leucoplastid. Attention should also be directed 

 to the fact that in some of the unicellular and filamentous algse 

 the pyrenoid divides during the division of the cell, thus behaving 

 like other protoplasmic organs. 



Inulin appears to be an isomer of starch and occurs in solution 

 in the cell-sap of parenchyma cells of stems and roots, being also 

 found in the medullary rays. It exists in greatest amounts during 

 the early fall and spring, being changed at other times to levulose. 

 In the Monocotyledons it is found in the Amaryllidaceae, Liliacese, 

 etc. In the Dicotyledons it is characteristic of the Compositae, 

 but also occurs in the following: Asclepiadacese, Bignoniaceai, 

 Cactaceae, Campanulace^e, Capri foliacese, Compositae, Cruci ferae, 

 Droseraceae, Euphorbiace^, Geraniaceae, Labiatae, Leguminosae, 

 Lythraceas, Magnoliaceae, jNIenispermaceae, Moraceae, Nepenth- 

 aceae, Passifloraceae, Ranunculaceae, Rubiaceae, Rutaceae, Salicaceae, 

 Santalaceae, Theaceae, Thymelaeaceae, Urticaceae, Valerianaceae, 

 Verbenaceae, V^iolaceae, etc. 



According to Dragendorft, there are two forms of inulin ; one 

 of which is amorphous and easily soluble in water, and another 

 which is crystalline and difficultly soluble in water. The latter 

 is probably, however, a modification of the former, and it is not 

 unlikely that the various principles known as pseudoinulin, inu- 

 lenin, helianthenin, and synantherin are all modifications of inulin. 



In examining fresh material (Fig. 92) the sections should be 

 mounted in as little water as is necessary to enclose the section. 

 If inulin is present it shows in the form of colorless, highly 

 refracting globules. The latter are usually relatively small and 

 tend to unite, forming one or more large globules. Upon increas- 



