52 



HARD WICKE ' S S CIENCE- G SSIF. 



NOTES FOR SCIENCE CLASSES. 

 Part II. 



[Continued/rom ^age ii.] 



IN tracing out the different parts in a long: section, is 

 more simple, than by a trans: section. If possible, 

 both sections should be exhibited at the same lesson. 

 It is, however, more difficult to cut long: sections than 

 trans:, especially of hard woody stems. The fact is, 

 it requires a little more patience. In cutting the lime, 

 it is well to use methylated spirit on the razor blade, 

 to float away the sections without injury. Invariably 

 use water for all sections of cellular tissue, such as 



and is composed of thin walled cells. 2 is the 

 cambium. 3. Xylem; examine this portion carefully, 

 find out the tracheids, lying near the cambium, then 

 the dotted and spiral vessels, lying near the pith. 

 4. Also find a portion of the medullary ray. 5 consists 

 of flattened muriform cells ; then we come to the 

 bark (phleum) ; look first at 6, which is soft bast, and 

 7, bast fibres, both combining to form the phleum. 

 Note the cork-cells, so as to recognise them in any 

 other section afterwards. Compare also the cortical 

 ground tissue, 8, containing chlorophyll, adjoining 

 the epidermis. 



Our next (fig. 39) is a section of the leaf of the 

 cherry-laurel ; this must be cut betwixt an incision in 



7 6 



Fig. 38. — Longitudinal Section of \Axae.{TiUa Enropcea). 



Fig. 40. — Transverse section of root of Iris. 



XT: 







90^ 





7 6 



Fig. 39- — Transverse section of Cherry-laurel leaf. 



herbaceous stems, or leaves, but methylated spirit for 

 ligneous sections. When cutting any section, hold 

 the razor handle firmly in the right hand, with the 

 blade resting on the first finger of the left hand, and 

 gently press the point towards the left shoulder ; never 

 do as inexperienced microscopists often attempt to 

 do, cut the section by pulling the razor in the direc- 

 tion of the right shoulder. With a little practice the 

 student will be able to cut excellent sections with ease. 

 Compare each portion of the cellular and vascular 

 tissue of the long: section with the trans:, so as to 

 make it familiar. First glance at the medullary open- 

 ing of the lime: — i. (fig. 38). It is a widening of the 

 medullary ray, which can be traced in the trans: 

 section, to its connection with the medullary sheath, 



a carrot root, as it is impossible to hold it in the hand 

 and take off the sections in water. Our object in 

 taking the specimen at this stage is to follow out the 

 position of the xylem and phleum respectively. The 

 phleum being on the outside of the fibro -vascular 

 ring, in exogenous stems, we should expect the same 

 position to be maintained in the leaf, thus it ought 

 to be found near the lower surface, and the xylem 

 next the upper surface. In preparing the section 

 let it be cut through one of the veins, near the 

 midrib. A good plan is to cut a square piece, about 

 the centre of the leaf, and place it in the carrot. 

 Begin to observe the different portions from the upper 

 surface : i will be the epidermis ; then, adjoining 

 this, will be, 3, cellular tissue (named from its resem- 



