268 



HARDWICKE'S SCIENCE-GOSSIP. 



NOTES FOR SCIENCE CLASSES. 



[Continued from page 249.] 



Part IV. 



COMPARE the longitudinal section of fern stem 

 (fig. 1S7) with the transverse section, note the 

 fibro-vascular bundles ; they are largely developed ; the 

 xylem contains the scalariform vessels, and is sur- 

 rounded by soft phloem. The apex of the stem 



The section is seen to be covered with hairs on the 

 epidermis ; stomata are found on the epidermis above 

 ground. Take a small portion of the section adjoin- 

 ing the phloem, beneath a higher power, to find the 

 sieve-tithes (fig. 188). No. 2 ; observe carefully their 

 position and construction ; they are placed between 

 the phloem. No. i, and xylem, No. 3. Also note with 

 care the structure of the scalariform vessels of the 

 xylem. 



I 



Fig, 



187.— Longitudinal section of underground stem of 

 Common Brake Fern (Pteris aquilinaj. 



Fig. 188.— Part of fibro- i 2 34 5 S 



vascular bundle of 



Pteris, more highly Fig. 189.— Transverse section of part 

 magnified. of petiole of Fern. 



Fig. 190.— Transverse section of stem of Selaginella, 



and root do not always form an apical cell, hence, 

 branching is rare ; it is never axillary, but always 

 dichotomous. 



No. I is a layer of dark yellowish cells, or 

 sclerenchyma ; 2 is the fundamental, or ground 

 tissue ; then we come to the fibro-vascular bundle j 3 

 IS the phloem portion surrounding 4, or the xylem 

 of scalariform ressels. 



Before leaving this part of our 

 subject, it would be well to take a 

 section from the petiole. Fig. 189 is 

 a transverse section of part of the 

 petiole, or stalk of the frond of the 

 common brake fern [Pteris aqitilina, 

 L.). No. I is the epidermis ; 2, 

 sclerenchyma ; 3, fundamental, or 

 ground tissue ; 4 is the phloem sheath; 

 5 phloem (bast), and 6 merely de- 

 notes the fibro-vascular bundle ; ob- 

 serve chieily the phloem sheath, and 

 ring of sclerenchyma in this section. 



The Selaginella is easily procured 

 from any nurseryman or gardener, 

 and is a very characteristic plant. 

 The stem is bilateral, with short 

 internodes, and small roundish leaves 

 generally in four rows. The root, 

 as well as the stem, branch dichoto- 

 mously in alternating planes. The 

 axis of the stem, in all the Lycopods, 

 is occupied by one or several vas- 

 cular bundles, separated from each 

 other by intermediate parenchymatous tissue. In the 

 Selaginella the bundle is connected with the epi- 

 dermis by a very loose spongy tissue, so that it 

 appears to lie almost isolated in a cylinder filled 

 with air, and connected with the walls only here and 

 there by parenchymatous cells. The structure of the 

 vascular bundle itself is always uniform ; the xylem 

 portion consists of wider vascular cells in its inner, 



