96 



PART II. THE INTIMATE STRUCTURE OF PLANTS. 



[23. 



FIG. 47. Restiug nucleus 

 from the young endosperm 

 of FritillariOi imperialist 

 (after Strasburger : x 1000) ; 

 showing the fibrillar Tiet- 

 work with its chromatin- 

 granules, and several nu- 

 cleoli. 



hyaloplasm lies a fibrillar network consisting of a substance termed 

 lint'n, in which are distributed a number of granules of a substance 

 termed chroma-tin. One or more small 

 granules, termed nucleoli, are to be seen 

 lying in the ground-substance, and consist 

 of a substance termed pyrenin. On treat- 

 ing the nucleus with staining reagents, the 

 fibrillar network becomes stained on 

 account of the absorption of the colouring- 

 matter by the chromatin-granules, as also do 

 the nucleoli. Its form is most commonly 

 spherical, but it may be lenticular, or 

 elongated, and straight or curved. 



A formation of a nucleus de novo does 

 not take place under any circumstances ; 

 hence all the nuclei in a plant have been 

 derived by repeated division from the nu- 

 cleus of the spore from which the plant has developed. The 

 division of the nucleus may be either direct or indirect (mitotic) ; 



in all cases it 



j\ divides into 



not more than 

 two parts. 



Direct divi- 

 sion or frag- 

 mentation of 

 the nucleus 

 commonly oc- 

 curs in old 

 cells (see p. 

 90), which 

 then become 

 multinucle- 

 ate ; it is not 

 associated 

 with cell-divi- 

 sion. So far 

 as the pro- 



Fia. 48. Direct nuclear division, in cells of old internodes of CGSS has been 



Tradescantia virginica: A drawn from fresh material; B isolated f ' f d 



nuclei, after treatment with acetic methyl-green. (After Stras- ' 



burger: x540.) it consists 



