288 SUMMARY OF CURRENT RESEARCHES RELATING TO 



BOTANY. 



A. GENERAL, including the Anatomy and Physiology 

 of the Phanerogamia. 



a. Anatomy. 

 CI) Cell-Structure and Protoplasm. 



Movements of the Nucleus.* — From observations made chiefly on 

 the mother-cells of stomates in Monocotyledons, H. Miehe concludes 

 that the changes in position of the nucleus are mainly due to growth- 

 processes in adjoining cells. The polar process may be reversed by the 

 action of centrifugal force, of traumatropic irritation, or of a reversal in 

 the direction of growth. The constant tendency of the nucleus to travel 

 to the upper portion of the cell is connected with the direction of growth. 

 If pieces of young epiderm are torn or cut off, an immediate movement 

 of the nucleus takes place through the membrane-pores ; as is the case 

 also with the mother-cells and the guard-cells of the stomates. Nuclei 

 of Hyacinthus under the influence of traumatropic irritation undergo a 

 change in the form and disposition of their contents. Traumatropic 

 movement of the nucleus may be attributed to a renewed growth of the 

 injured zone caused by the injury. Under favourable conditions the 

 epiderm possesses a power of regeneration. 



Development of Karyokinetic Spindle in Pollen-mother-cells of 

 Lavatera.f — Miss Edith S. Byxbee thus sums up the results of her ob- 

 servations on the development of the karyokinetic spindle in the pollen- 

 mother-cells of a species of Lavatera. The cytoplasm of the young 

 pollen-mother-cell is made up of two constituents, a fibrous network and 

 a granular substance. The following are the steps by which the spindle 

 is formed. The meshes of the network close to the nuclear wall puil 

 out in the direction parallel to the wall, forming a felt of fibres round 

 the nucleus. The granular constituent of the cytoplasm collects in the 

 wide dense zone round the nucleus. The liniu increases in quantity. 

 The nuclear wall breaks down, and the fibres outside begin to grow into 

 the nuclear cavity. The cytoplasmic and linin fibres form a mags in 

 which the chromosomes lie. The mass of fibres projects out at a 

 number of points, forming the multipolar spindle. Two of the cones 

 become more prominent than the others, which they finally absorb, thus 

 forming the bipolar spindle. In the second division of the pollen-mother- 

 cells the process is exactly repeated. The granular substance which 

 forms the dense zone is comparable to the deutoplasm of the egg in 

 animals. Finally, the spindle is formed directly from cytoplasmic 

 elements and linin network present in the cell from the first, and not 

 from any special spindle-forming substance, or by the aid of centro- 

 Bomes. 



* Flora, lxxxviii. (1901) pp. 105-42 (1 pi.). 



t Proc. California Acad. Sci., ii. (l'.)OO) pp. 63-76 (4 pis.). 



