CELL-CONTENTS AND CELL-WALLS. 29 



roots of Hyacinth or of Onion, obtained by growing the bulbs in 

 hyacinth-glasses containing culture solution, may be used. The 

 tip (about an inch) of a growing root is cut off, and the tips are at 

 once transferred either to absolute alcohol (or strong methylated 

 spirit), or (if the mitotic figures are to be obtained with certainty) 

 to a fixing solution containing 10 parts by volume of 2 per cent, 

 osmic acid, 4 parts of 10 per cent, chromic acid, 3 parts of glacial 

 acetic acid, and 20 parts of water. If the latter fixing solution is 

 used, the tips must be left in it for about 12 hours, then transferred 

 to water and thoroughly washed for several hours, then hardened 

 by being placed in increasing strengths of alcohol 70, 80, 90 per 

 cent., and finally absolute alcohol, for a few hours in each case. 

 After this, they are transferred to methylated spirit, and sections 

 cut in split pith. After staining, the sections should be treated 

 with absolute alcohol, cleared with clove oil, and mounted in 

 balsam. 



Preparations of root-tips, cut with the microtome and doubly 

 stained, may be purchased The details of mitosis are given in 

 text-books, and most of the stages may be traced in successful 

 preparations made from root-tips. 



(d) Direct division (fragmentation) of the nucleus may be 

 observed in the large internodal cells of Nitella, or in longitudinal 

 sections of the stem of Tradescantia and various other plants. It 

 takes place chiefly in old cells, which have ceased to undergo cell- 

 division. The nucleus becomes elongated and dumbbell-shaped, and 

 finally constricted into two, in much the same way as a dividing 

 chloroplast. 



II. STREAMING MOVEMENTS OF PROTOPLASM. 



28. Streaming Movements of living protoplasm, 

 rapid enough to be watched under the microscope, are 

 well shown in the long cells of the Stoneworts Nitella and 

 Chara, and in the leaf of Elodea. This streaming, or 

 cyclosis, may also be studied in the plasmodium of 

 Myxomycetes ; in the Desmid genus Closterium ; in the 

 mycelium of Mucor ; in the epidermis torn from the 

 inner scales of an Onion bulb ; and in hairs found on 

 the roots, stems, leaves, and flowers of various plants. 

 It will usually be found that the movements can be 

 started or, if already in evidence, hastened by warming 

 the preparations or by using warm water to mount the 

 objects in. 



