HARDWICKE'S SCIENCE-GOSSIP. 



53 



blance to wooden palings, palissade tissue), it is packed 

 closely, like eggs in an Irish crate, hence the upper 

 side of a leaf is darker in colour than the lower ; 



4 is spongy cellular, or ground tissue ; here we trace 

 abundance of air spaces, then we come to the lower 

 •epidermis, 2 ; note the difference. The next and 

 most important partis the fibro-vasc: bundle. When 

 seen under a low power, it has a whitish appearance. 



5 is the xylem ; observe the spiral vessels, much 

 darker than the phleum. They are traced clearly, if 



I e 3 'V 5 C 7 

 Fig. 41. -Longitudinal section of Iris root. 



Fig. 42. — Transverse section of radicle of Kean. 



stained by running a drop of weak solulion of 

 magenta, under the cover-slip ; the phleum, 6, is 

 formed of soft bast only. Now note the guard cells of 

 the stoma, No. 7. 



Before proceeding further, we should advise the 

 student to study the root ; an excellent specimen 



may be secured at any time from the garden Iris 

 (/. Gcrmanica, fig. 40). It is best cut with water on the 

 razor blade, then float it off, in a watch glass, and 

 select the best sections for study. No. i is the thick 



epidermis ; 2 and 7, both ground tissue ; in 7 it takes 

 the form of packing parenchyma ; 3 is the bundle- 

 sheath ; 4, pericambium ; these are very thin, transpar- 

 ent, and fragile cells ; 5 and 6, xylem, but of different 

 vessels, as will be observed in the long: section ; 

 5 are spiral, and 6, pitted vessels. In the long: sections 



(fig. 41), compare with trans: The same numbers are 



employed to explain each part. 



Examine also an exogenous root ; place the garden- 

 bean in a small quantity of water, and allow it to 

 germinate on the mantelshelf; when the radicle has 

 made considerable growth, make a few sections. 

 Take a portion near the coUum, and trace out the 

 entire trans: section under a low power, after 

 staining it with magenta. This is a simple and 

 pleasing operation ; drop a small quantity on the slide 

 close to the cover slip, allowing it to run in contact 

 with the section ; then place a strip of blotting- 

 paper on the opposite side to extract the magenta, it 

 will stain the xylem a bright pink, thus rendering 

 it unmistakable. 



Fig. 43. — Transverse section of radicle of Bean, to explain 

 growth of root. 



Observe, in the entire section. No. i is the epider- 

 mal layer ; 2, ground tissue ; 3 and 4, xylem ; note 

 the spiral vessels in the latter, in a long: section ; 

 5 is the phleum. Now cut another trans: section, to 

 explain the growth of a lateral rootlet, cutting it from 

 the radicle, through the small protuberance, detected 

 in abundance, on the older part, and immerse the 

 section for a few minutes in a strong solution of 

 potash in a watch-glass. No. i is the growing-point 

 of the rootlet ; note its position, and where it takes 

 its rise above the spiral vessels of the xylem, in the 

 old radicle ; 2 is the epidermal layer of the mother- 

 root ; 3, ground tissue, and 4-4, xylem. The 

 phleum is not so readily detected in the radicle, it is 



easily made out in the old root. 



R. 



White Calluna. — In reference to query in the 

 December number of Science-Gossip respecting a 

 white variety of Calluna vulgaris, may I say that I 

 have found it several times on the Sidlaw Hills (For- 

 farshire), but it is uncommon, and its possession is 

 considered in Scotland as likely to render the possessor 

 "lucky."— il/. E.Pope. 



