132 R. BRAITHWAITE ON THE HISTOLOGY OF PLANTS. 



carbo-hydrates, and in a more advanced stage it consists of pure 

 cellulose, but in the youngest state of develoj)raent it appears to be 

 intermediate between this substance and starch, which in a few 

 cases, as in fungi and the cambial walls of tissue cells is not further 

 altered, and is believed by Wigand to consist of Bassorin. Neither 

 the solution of chloro-iodide of zinc, nor aqueous sol. of iodine with 

 sulphuric acid, give any colour to the entire cambial cell-case of 

 completed tissues ; but in AlgJE, where the cellulose case is distinct 

 and firm, or where, as in the young tissues, the primary cellulose 

 case is deposited within the cambial wall, Schultz's test produces 

 a more or less blue coloration. 



3. The Cell Nucleus — Cytoblast of Schleiden — occurs in the 

 living cells of all plants, though in fungi and lichens it cannot 

 always be detected. The nucleus is best observed in loose, soft 

 tissues, as cucumbers, beans, stems of liliaceous plants, and the 

 young hairs on leaves and sepals. In form it is lenticular or sub- 

 globose, and its position is usually close to the internal wall, 

 or more rarely near the centre of the cell. In many cases a true 

 membrane invests the nucleus, but in others it cannot be demon- 

 strated, though most probably it is always present, and in the 

 fluid, granular, or waxy contents, lies another important element 

 — the nucleolus, either single, in pairs, or many to each nucleus. 

 In its chemical reaction the nucleus entirely agrees with the pri- 

 mordial membrane. Solution of carmine is readily taken up by it, 

 the nucleolus being most strongly coloured ; an immersion for 24 

 hours is necessary, and then washing in water with a few drops of 

 acetic acid. 



4. The Cell Contents, — These may be distinguished into 

 Protoplasm, a viscid, granular fluid, forming a layer next the wall, 

 and Cell sap, more watery and occupying the inner space of the 

 cell. Certain firmer organic and inorganic contents are also found 

 suspended in the fluid contents. Protoplasm almost completely 

 fills the young cell, and from it, in course of development, the 

 cell-sap separates into the interior. At this time also in the denser 

 protoplasm, vacuoles or small cavities arise, which are separated 

 from one another by bars of protoj^lasm, broadest at first, and are 

 filled with the fluid sap. Where the nucleus is in the centre of 

 the cell part of the protoplasm collects round it, while another 

 portion is retracted to the inner surface of the membrane, the two 

 being connected by the bars or finer threads of protoplasm, which 



