28 



HARDWICKE'S SCIENCE-GOSSIP. 



and pith, they accompany the fibro-vascular bundles 

 into the leaves. 



Laticiferous vessels are distinguished from vessels 

 containing raphides only by the absence of these 

 crystals. (See fig. 25, raphides from stem of Trades- 

 eantia. No. I, the crystals, or raphides.) These 

 vessels are detected in the outer bark, also in the 

 leaves of many Monocotyledons. A beautiful speci- 

 men may be obtained from the decaying petiole of 

 the rhubarb, mounted as an opaque polariscopic 

 object. The crystals of oxalate of lime are really 

 magnificent, when exhibited by an artificial light. 



Whilst we have the Trade scantia Virginiea, a plant 



termed rotation, as in Chara or Valisneria ; less 

 often, as in the filaments of Tradescantia, it passes in 

 threads and bands transversely through the cell-sap, 

 and is then termed circulation. The currents are 

 apparently irregular, sometimes suddenly arrested, 

 then commencing again with greater rapidity. 



The old term spongiole, as applied to the growing 

 point of the rootlet, is now expunged from our 

 modern text-books ; still the student should learn to 

 distinguish the root-cap, especially its form and com- 

 position. The essential peculiarity in the roots of all 

 Dicotyledons, is the root-cap. (See fig. 26, root-cap of 

 Pontederia. I is the root-cap ; 2, growing-point, 



fig. 25. — Raphides in stem of 

 . r Tradescantia. 



Fig. 36. — Root-cap of Pontederia. 



Fig. 27. — Pollen-tube of the Evening Primrose. 



Fig. 28.— Circulation of Protoplasm in Tradescantia. 



found commonly in cottage gardens, under examina- 

 tion, it would be well to bring before the student 

 the circulation of protoplasm observed in the hairs on 

 the .filament (fig, 28).' ■ It is only requisite to cut off 

 the hairs from.a.flower just expanding with the razor,' 

 and place it with a drop of water on the slide j^the 

 deep-pink cell ; walls' are sufficient .to. bring .out 

 clearly the cell contents, without any staining-fluid. 

 1 is the cell-wall; 2, the. vacuole:; , and. 3, the proto- 

 plasm in active motion, .moving around the vacuole. 

 The protoplasm .which .'is .enclosed in 'a cell .wall 

 has no power of escaping -from its envelope. The 

 course of the current is usually along the Wall, and., 

 in simple spiral or reticulate lines, and is then 



and 3, young root, composed of cellular tissue.) 

 Beneath this root-cap, as it is termed, the production 

 of new cells continues, whilst the cap itself acts as a 

 protecting shield to the root. As many village 

 students will be unable to procure the pontederia, 

 the duckweed (Lem/ia. minor). will equally well ex- 

 plain its nature and structure. 



, About the best, specimen with which .we are 

 acquainted for exhibiting the pollen-tube, is the. 

 evening primrose (Oenothera biennis). , Secure a 

 flower early. in the morning, when it has just begun 

 to droop ; for the petals are only open one evening ; 

 and having cut away the stamens^and petals, make 

 a transverse section down the style ; this requires a 



