138 R. BRAlTflWAITE ON THE HISTOLOGY OF PLANTS. 



In Monocotyledons, especially Liliticcje, Araccae, and also in 

 Cactaceaj, the crystals are in form of long needles, termed Raphides, 

 which lie parallel in bundles, and often fill the elongated cells, 

 especially in autumn, though during active growth they may be 

 entirely absent. In the Fungi and Lichens, the crystals are usually 

 very small, and not enclosed in cells, but collected outside the cell- 

 wall. In the walls of thick fusiform cells (Spicular cells) of the 

 curious plant Welwitchia mirahilis, Dr. Hooker detected numerous 

 scattered rhombic crystals, and Millardet found similar crystals in 

 the bast-cells of the bark of Acer pseudoplatanus. 



In active protoplasm currents sometimes occur small crystals, as 

 in hairs of the cucumber plant, where they are octohasdral. These 

 usually occupy the cell lumen, and are enclosed in a very thin 

 envelope, which is probably the true condition in all cases. Car- 

 bonate of lime has been found by De Bary, as distinct crystals in 

 Physareae, and as little nodules or cystoliths in certain cells of 

 species of Urtica, Ficus, and Acanthaceee. In still finer division 

 and entering into the structure of the commissures of the cell-walls, 

 carbonate of lime is found in many Algae, as the species of CoralUna^ 

 Jania, and Melohesia, which on this account are highly fragile, and 

 of stony consistence. 



ILLUSTRATIVE FIGURES AFTER SACHS. 

 Plate 6. 



Fig. 1.— Young Pollen cell X 670. A, invested by the membrane only. B, after 

 the cellulose case has formed. C, ditto, after treatment with Sol. 

 Iodine, — n. nucleus, c. cellulose case, $. primordial utricle, i^. proto- 

 plasm. 



Fig. 2.— Parenchymatous cell of flower stalk of Tradescantia Virginica, with a 

 siuipl ■ spiral parietal cuirent of protoplasm ; )i. nucleus, p. protoplasm, 

 cl chlorophyl. X 420. 



Fig. 3. — Cell of staminal hair of same, showing internal currents. X 6C0. 



Fig. 4.— Cells from stem of germinating onion ; a. the yellow protoplasm invests 

 the central nucleus, and sends filaments toward the wall ; b. an older 

 stage, the nucleus applied to the wall, fine threads of colourless pro- 

 toplasm, chlorophyl fully formed, and lining the wall. 



Fig. 5. — Starch granules X 66' >. A. from Turmeric. B. from stem of Sarsa- 

 parilla. C. from milky sap of Euphorbia splendens. 



Fig. 6.— Very thin section of cotyledon of Pea, showing starch granules in sec- 

 tion. X 800. 

 Fig. 7. — Two cells of Dahlia root treated with alcohol, and showing Inulin ; 



a. in water, h. after application of nitric acid. X 420. 



Fig. 8. — Crystals X 320. a. single octohedron from leaf of Begonia heracleifolia ; 



b. crystal cluster from the same j c. cell with raphides from stem of 

 Aloe retusa. 



