46 CELLULAR TISSUE. 



The chief place where they occur is the green leaf, surrounded by air, especially 

 the leaves of land plants and floating water plants. Certain land plants destitute of 

 chlorophyll, viz. INIonotropa Hypopitys and Neottia Nidus avis ^ have no stomata 

 at all. With the exception of the pistil Lathraea squamaria is without stomata ^. 

 On the contrary, on the leaf of Lathraea clandestina ^, as also of the Orobanches * 

 and Lennoacese ''j they occur in considerable numbers, on that of the Cuscuteae * at 

 least here and there. 



On Rhizomes*' growing in the ground they are not uncommon, at least in 

 isolated cases ; e.g. the young potatoe before formation of the cork-layer ', the 

 tuberous stem of Herminium ]Monorchis ^ the rhizome of Epipogon, &c. 



In parts which are submerged air-pores are as a rule completely absent, but 

 here also exceptions occur. They are to be found regularly on the submerged 

 primordial leaves and the germinal leaf of the Marsiliacese ^, on the submerged leaves 

 of the Calilrichineae, Sect. Eucallitriche^"; Askenasy " found single ones on the 

 cotyledons of Ranunculus aquatilis normally unfolded under water. The statement 

 of H. Weiss on their occurrence on submerged parts of Najas and Potomageton is 

 not confirmed. 



~^-'- In water-plants whose leaf can vegetate either submerged or in the air, as 

 Ranunculus aquatilis, the Callitrichineae, Hottonia, Myriophyllum, Marsilia, &c., the 

 occurrence or distribution of air-pores varies according to the above-stated habit. 



The air-pores occur (perhaps with exception of single cases of their solitary 

 appearance on submerged parts) only where intercellular spaces, containing plenty 

 of air, are present in the tissue covered by the epidermis. Still stomata are not 

 always present where the latter is the case. Where tissue rich in air alternates with 

 tissue with httle or no air (Sclerenchyma, Collenchyma) there is as a rule in the 

 epidermal tissue covering them a corresponding alternation of spots with and without 

 stomata ^'^. Connected with these are the universal phenomena of absence of stomata 

 on the nerves of leaves ; their occurrence near and between these, their absence on 

 the channels and edges of channelled leaves, petioles, stems, and their presence 

 in the surfaces, or furrows alternating with these ; (e.g. leaves of Bromeliaceae, Phor- 

 mium, Grasses, stems of the Umbelliferse, Equiseta, &c. : stomata-bearing bands 

 and spots on the young shoots of Hedera, Juglans, Populus ", on the sides, and at the 



plants, ia others they are absent. Compare Rudolphi, Anatomic, pp. 85-91 ; Treviranus, Verm. 

 Schriften, p. 50; H. Krocker, de Plantar. Epidermide (1833), p. 16: A. Weiss, Verhandl. Zool. hot. 

 Vereins in Wien, 1857; and especially Hildebrand, Einige Beobachtungen aus der Pflanzen-Ana- 

 toraie (1861). ' Rudolphi, Anatomie d. Pfl. (1807), p. 66. 



^ [Krause, Beitr. z. Anat. d. Vegetationsorg. d. Lathrsea Squamaria. Diss. Breslau. 1879.] Bow- 

 man, Trans. Linn. Soc. London. XVI. 



' Duchartre, Sur la Clandestine de I'Europe. Mem. de I'lnstitut de France, 1848. 



* Unger, Exantheme d. Pfl. p. 49. 



'•> H. Graf zu Solms-Laubach, Die Lennoaceen (Halle, 1871). 



* Hohnfeldt Botan Zeigt. 1881, p. 38. ' Caspary, Botan. Zeitg. 1857, p. 117. 



* Prillieux, Ann. sci. nat. 5 Ser. IV. p. 265, pi. 15. 



* A. Braun, Monatsbr. d. Berlin. Acad. 1870, p. 665. 



*" Hegelmaier, Monographic der Gattung Callitriche, p. 10. ^' Botan. Zeitg. 1870, p. 198. 



^'^ [Cf. Potonie, Beziehungen zw. d. Spaltoffnungsystem u. d. Stereom. b. d. Blatt-Stielen d. 

 Filicineen, Ref. Bot. Centralbl. i88r. Bd. 8. p. 70] 



^ Compare Trccul, Comptes rendus, lorn. 73, p. 15. 



