48 CELLULAR TISSUE. 



Of the memibers surrounded by air, stems bearing chlorophyll are rich in 

 stomata if leaves are absent : e.g. Equisetum, Salicornia, Casuarina, Colletia, 

 Cactacese, &c. There are eighteen stomata on i"^"! a in Cereus speciosus (Krocker). 

 Leafy stems also, whose own foliage-surface is relatively very large, are rich in 

 stomata, e.g. Campanula patula, linifolia, Salvia glutinosa, Polygonum aviculare, Vicia 

 Faba, segetalis, Epilobium palustre, Capsella Bursa Pastoris, IMohringia trinervia, 

 Linum catharticum, Potentilla aurea, and many others (Unger, Exanth. pp. 98-137). 

 Unger ascribes numerous stomata to the green branches of ligneous plants, such as 

 Vaccinium IMyrtillus, Rhamnus cathartica, and Frangula. Morren found in Prunus 

 Mahaleb 18, and in Rosa damascena 36 on each i™'"a. Similar large numbers 

 are found in related species, in Viburnum opulus, &c. (Stahl, Botan. Ztg. 1873, 

 p. 578). In very many plants, on the other hand, very scattered stomata occur on 

 the stems ; e.g. in Prunus domestica seven, in Solanum tuberosum four on each 

 iraniQ , or still fewer; only in rare cases there are none at all. 



From occasional observations on the petiole similar results are obtained as for 

 the stem. 



Numerous observations of their number and distribution have been made on the 

 parts where they occur in largest numbers, viz. the laminae of green foliage leaves of 

 land and aerial plants. The older observations of Hedwig, Von Humboldt, Sprengel, the 

 copious works of Rudolphi, and other more scattered notices, have been followed more 

 recently by the works of H. Krocker, Unger, A. Weiss, E. Morren, Czech, and Karelst- 

 schikoff^. The very full statistics of Weiss inform us that of 157 species of land plants 

 investigated, the mature foliage leaves have on an average on the space of i""™ D 



less than 40 stomata in 12 Species 



40—100 „ „ 42 „ 



100 — 200 „ „ 38 ,, 



200—300 „ „ 39 ,, 



300—400 „ „ 12 „ 



DD 



O „ ,, I 



more than 600 „ „ 3 „ 



The distribution of the air-pores over the surface of the leaf is in land plants directly 

 connected with that of the air-containing intercellular spaces. It diiTers therefore ac- 

 cording as the leaf shows a bifacial or centric arrangement of the chlorophyll-con- 

 taining parenchyma, and depends in individual cases upon the number and width of the 

 lacunae in this tissue. (Comp. Chap. IX.) 



Herbaceous, flat, horizontal leaves with bifacial arrangement of the Parenchyma have 

 usually stomata on both surfaces. Of 466 such species KarelstschikofF found this to be 

 the case in 450. But of these 37 have on the upper surface only very few, often only 

 solitary ones, lying near the nerves : and the majority are much poorer in stomata on 

 the upper than on the under surface. 



Firm, leathery, horizontal, also bifacial leaves, with smooth, shining upper surface, as 



* K. Sprengel, Anleitung z. Kenntn. d. Gevvachse, I. — Unger, Exantheme der Pflanzen (1833). 

 Anat. und Physiol, d. Pfl. pp. 193, 334.— Compare on the older lilerature, Meyen, Phytotomie, 

 p. 108 ; E. Morren, Determination des Stomates de quelques vegetaux. Bullet. Acad. Bruxelles, 

 torn. XVI (1864) ; Czech, Ueber Zahlenveihaltnisse und Vertheilung d. Spaltofliiungen, Botan. Zeitg. 

 1865, p. loi ; A. Weiss, Ueber die Zahlea- und Grossenverhaltn. d. Spaltoffnungen, Pringsheim's 

 Jahrb. Bd. IV; Karelstschikoff, Ueber d. Vertheilung der Spaltoffnungen auf d. Blattern, Bulletin 

 Soc. Hist. Nat. de Moscou, 1866. For many details we must here refer to these works, which do not 

 by any means coincide on all points. 



