60 



BOTANY 



PART I 



nuclear cavity, which is filled with nuclear sap and surrounded by 

 a membrane (w). The nuclear membrane, strictly speaking, is a part 

 of the surrounding cytoplasm, and is the protoplasmic layer by 

 which the cytoplasm separates itself from the nuclear cavity. The 

 nucleus in young cells with abundant protoplasm is, as a rule 



spherical. When situated in the lining layer 

 of cytoplasm of older cells, it is frequently 

 of a flattened form, while in elongated cells 



it exhibits a corresponding elongation. Ex- 

 ^'-^ ceptionally in old cells the nucleus is forked, 

 J, lobed, or of some other irregular shape. 

 " These changes in form of the nucleus are 

 due to slow movements, which cannot, as a 

 rule, be directly observed. In embryonic 

 tissues the nuclei are relatively large in pro- 

 portion to the size of the protoplasts. 

 Glandular cells are also usually provided with 

 larcre nuclei. 



While the cells of 

 the Cormophytes are 

 almost always uninu- 

 cleate, in the Thallo- 

 phytes, on the con- 

 trary, multinucleate 

 cells are by no means 

 infrequent. In the 

 Fungi, and in the 

 Siphoneae among the 

 Alga?, they are the 

 rule. The whole 

 plant is then com- 

 posed either of but 

 one single multi- 

 nucleate cell, which 



Fig. 60 -A cell of Cladoplwra ^g extensively 



glomerata, fixerl with 1 per cent ■,■,■■ -i 



chromic acifl ami stained with brancnecl anCl ex 



carmine. )i Nuclei ;c;i, chroma- hibit a complicated 

 es; p, pyrenoids; «, f 1 f^^.^^ (ficr 



grains, (x 540.) CXtei IIcU lUiiii \J- i)^- 



286), or it may con- 

 sist of a large number of multinucleate cells, forming together one 

 organism. Thus, on suitable treatment, several nuclei may lie de- 

 tected in the peripheral cytoplasm of each of the cells of the common 

 filamentous fresh-water Alga Cludophoni glomerata (Fig. 6, p. 1 2, Fig. 60). 

 The nuclei of the long, multinucleate cells (Fig. 61 n) of fungal 

 filaments, or IIYPIIAE, and also of many Siphoneae, are characterised 

 by their minute size. 



tophoret 

 starch grains. 



Fio. 61. — Portions of two ad- 

 jacent cells in a hypha from 

 the stalk of Fsalliota ar- 

 vensis. n, Nuclei ; m, pits. 

 (X 540.) 



