31] 



CHAPTER II. THE TISSUES. 



115 



drop; Leucojum vernum, the Snow-flake;) or transversely (e.g. Iris germa- 

 nica. Erythronium Dens-Canis, species of Gladiolus and Tritonia). 



Tin' colourless mesophyll of succulent and coriaceous leaves consists of 

 large cells containing much watery sap constituting in fact an aqueous 

 tissue (e.g. leaves of Alo'^, Mesemhiyanthemum, some Myrtaceae etc.). 

 In some Orchids (e.g. Oncidium maximum), the cells of the aqueous tissue 

 are scatterecFamong the assimilatory cells ; in many Orchids the cells of 

 the aqueous tissue are tracheidal, having spirally-thickened walls, as they 

 are also in the stem and leaf of Nepenthes. 



In jirainvjcases, especially in aquatic plants, the ground-tissue 

 has large air-cavities, either lysigenous or schizogenous (see p. 

 N!i : generally 

 , they 

 schizo- 

 genous origin in 

 aquatic plants, 

 of lysigenous 

 origin in land- 

 plants. These 

 cavities fre- 

 quently extend 

 throughout the 

 whole length of 

 the root or the 

 leaf and through 

 an entire inter- 

 node of the 

 stem ; but they 

 may be inter- 

 rupted at inter- 

 vals by__dia- 

 p h r a g m s (e.g. 

 leaf of some 

 Monocotyledons ; 



root of Hydrocharis ; stem of Alisma, Pontederia, Marsilea). 

 When these cavities^are largely developed the member becomes a 

 float (e.g. root of Jussisea). 



4. The^Endodermis is, in the great majority of cases, a single 

 layer of cells ; it is but rarely altogether wanting ; it sometimes 

 consists of t\vo layers, formed by the tangential division of the cells 

 of the primitively single layer (e.g. root of Equisetum ; stem of some 

 Pteridophyta, such as Aspidium, Pteris, Salvinia and Azolla). 



td 



Fio. 94. -Trans verse section of central portion of the root of 

 Bonunculus repent (x 300): ed the endodermis, enclosing the 

 single central stele ; its radial walls show the sections of the 

 cuticularised thickening-bands ; x the four protoxylem-bundles ; 

 t the solid xylem; s the four phloem-bundles ; pc the pcricycle ; 

 r the cortical tissue. 



