R. BRAITHWAITE ON THE HISTOLOGY OF PLANTS. 137 



is left behind in lenticularly flattened granules, -0075 — '009 mm. 

 in diameter ; sucli are fomid in the full- formed leaves of Tulip, 

 Holly, Sedum acre, &c. 2nd, the substratum on which chlorophyl 

 is deposited, consists of one or more starch granules of various 

 forms, and this kind alone is found in the leaves of mosses and 

 Hepatica?, and the leaves of Mistletoe and IIo?/a carnosa. 



To return to tlie origin of chlorophyl, it is clear this must be 

 observed in the earliest development of germinating plants. We 

 find that the first kind of chlorophyl granules proceeds from colour- 

 less protoplasm, either homogeneous, or with very fine molecules, 

 and while it is acquiring a yellow-green colour it is formed into 

 small spherical masses, which later become overlaid by the entirely 

 green colouring matter. In the second kind the starch granules 

 appear after the chlorophyl granule is formed. 



The origin of starch in chlorophyl is as follows : — In the perfect 

 chlorophyl grain, there appear within the homogeneous mass one 

 or more granules, which gradually enlarge and distend the grain, 

 so that the enveloping green layer thins away, and at last dis- 

 appears, and the free starch granule becomes visible. When the 

 chlorophyl grain contains several starch granules, as these increase 

 in size, they become flattened on the sides touching each other, and 

 thus acquire polyhedral facets, while the free outer surface remains 

 spherical. It is needless to add that extremely fine sections, and 

 high magnifying power are requisite for these observations. 



Colouring Matters. — These occur as evident cell contents, 

 either dissolved in the cell sap, or, like chlorophyl, collected in a 

 granular protoplasmic form ; the pure blues and red as a rule occur 

 in the former state, the yellows in the latter. Wigand believes 

 that the blue and red matters (Anthocyan) owe their origin to 

 Tannin, the yellow (Anthoxanthin) to Chlorophyl. 



Crystals. — The crystals appearing as cell-contents are usually 

 oxalate of lime ; but tartrates and citrates are also met with. 

 Crystals only occur in parenchymatous tissues, and are found in 

 almost all flowering plants, in Fungi and crustaceous Lichens, but 

 not in Algae, Mosses, or Ferns. 



The crystals may be single, or in pairs, as in Begonia, and in 

 gemiinating plants of Fhaseolus ; more frequently they occur in 

 groups of numerous crystals (Sphceraphides of Gulliver), which are 

 usually deposited round a nucleus of organic matter, as in Rhubarb, 

 Hoya, the leaf of Begonia, and stem of the India-rubber plant. 



