STOMATA. 



[ 621 ] 



STRIATELLA. 



appears to be uncertain. Mohl and other 

 authors assert that the " guard-cells " origi- 

 nate from one of the cells of the subepi- 

 dermal tissue, which is pushed up into a 

 vacancy formed by the separation of the 

 epidermal cells at certain points. This cell 

 is said to be next divided into two, which 

 become free from each other in the line of 

 the new partition then formed. Nageli and 

 others assert that the guard-cells are origin- 

 ally constituent cells of the epidermal layer 

 which become subsequently displaced down- 

 wards (or upwards), and undergo special 

 development analogous to that just described. 

 Dr. Garreau has recently described this mode 

 of development as occurring in Tradescantia. 

 We believe it is the correct view, at all 

 events in some cases, but the appearances 

 are certainly difficult to explain on this plan 

 in the Iridaceae, Equisetacese, and some 

 other plants. 



The stomata are generally largest upon 

 succulent leaves, smallest on hard and 

 leathery kinds ; their form and number are 

 most varied, both in different plants and 

 on different parts of the same plant. They 

 abound most on the lower face of leaves, 

 but it has been mentioned that they are not 

 found on submerged organs, and on floating 

 leaves they occur only upon the upper face. 

 The larger kinds are more scattered on 

 a given surface, the smaller occur closer 

 together (this depends, of com-se, on the 

 general character of the epidermal and sub- 

 jacent tissue). The numbers have been 

 estimated upon the surfaces of many leaves, 

 of which a few examples may be given ^ 

 thus a square inch contains in — 



Upper siirface. Lower surface. 



Carnation 38,500 38,500 



Garden Flag 11,572 11,5/2 



House-leek 10,710 6,000 



Tradescantia 2,000 2,000 



Misletoe 



Holly 



Lilac 



Vine 



Laurestinus 



200 200 



63,600 



160,000 



13,600 



90,000 



BiBL. General Works on Struct. Botany ; 

 Krocker, De Epidermide, Vratisvl. 1833; 

 Mohl, Verm. Schrift. pp. 245, 252, Bot. 

 Zeit. iii. p. 1 {Ann. Nat. Hist. xv. p. 217) ; 

 Nageli, Linnaa, xvi. p. 237. 1842; Mirbel, 

 sur Marchantia, Mem. Acad. Roy. France, 

 xiii. ; Gasparrini, Nuove ric. v. strutt. d. Cis- 

 tomi, Naples, 1844; Garreau, Ann. des Sc. 



nat. 4 ser. i. p. 213; J. D. Hooker, Flora 

 Antarct. i. p. 291 ; Golding Bird, Proc. 

 Linn. Society, i. p. 290 ; Stocks, MS. 



STONES, OF Fruits, such as cherries, 

 plums, &c., afford excellent materials for 

 sections, showing extreme development of 

 the woody Secondary deposits of vege- 

 table cells. 



STRIARIA, Grev.— A genus of Dictyo- 

 siphonaceae, nearly related to Punctariacese 

 (Fucoid Algae), having a branched, filiform, 

 tubular frond, arising from a shield-shaped, 

 naked disk. The walls of the tube are mem- 



Fig. 712. 



Fig. 713. 



Fig. 714. 



Striaria attenuata. 



Fig. 712. Part of a frond. One-third of the nat. size. 

 Fig. 713. A fragment of the sori. Magnified 5 dianis. 

 Fig. 714. Section of a fertile branch, with sori. Mag- 

 nified 25 diameters. 



branous, and the cavity without septa. S. 

 attenuata (fig. 712) grows from 3 to 12" 

 high. The branches are attenuated towards 

 each end, and marked with rings consisting 

 of clusters of oosporanges (" spores ") (fig. 

 713), sometimes accompanied by filaments 

 (fig. 714). Colour pale olive. 



BiBL. Harv. Brit. Mar. Alg. p. 41. pi. 

 8 A ; Grev. Brit. Alg. fig. 9. 



STRIATELLA, Kiitz.— A genus of Dia- 

 tomaceae. 



Char. Frustules with a stipes attached to 



