ZOOLOGY AHD BOTANY, MICROSCOPY, ETC. 51 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Cytology, 

 including' Cell-Contents. 



Chromosomes of Allium.* — D. M. Mottier and M. Nothnagel 

 have studied the mitosis of the pollen-mother-cells of Allium csmuum. 

 The results of the investigation differ in many points from those 

 obtained with A . Gepa, and are as follows : — Prior to synapsis the 

 nucleus consists of a network of linin and chromatin grannies, with 

 one or more nucleoli but without knots, and there is a tendency to 

 form a continuous spireme. During synapsis there is no union of two 

 spiremes, but a real contraction of the nuclear network, and the spireme 

 is a direct transformation of the latter. The hollow spireme is a thick 

 chromatin cord, and where splits are present these always close before 

 cross-segmentation. A rearrangement of the spireme takes place, 

 resulting in an entanglement of loops and parallel parts twisted upon 

 one another, and during this process transverse division occurs Each 

 bivalent chromosome results from the approximation, usually side by 

 side, of different lengths of the spireme, and may therefore be regarded 

 as two somatic chromosomes that were previously arranged end to end. 

 The prevalent form of bivalent chromosomes is that of a large ring. 

 The daughter-segments split longitudinally' during metaphase. pre- 

 paratory to the second or homotypic mitosis. In the daughter-nuclei 

 the chromatin segments elongate, become waved, and form an inter- 

 rupted spireme by the union of the free ends. This spireme forms a 

 crown open at both the polar and antipolar sides, and there is no fusion 

 of the ends into knots. 



Relation between the Nucleus and Crystal-formation.t — J. A. 

 Samuels has studied the cytology of the nucleus in connexion with the 

 development of crystals in the cells of the perianth of Anthurium. 

 Polyhedral crystals are very numerous in the outer cells, less numerous 

 in the more internal cells ; raphides occur less frequently, and are 

 found in the central cells of the bracts of the perianth. At the time 

 of crystal-formation the protoplasm accumulates in the cell, while the 

 nucleus takes up a peripheral position where the cytoplasm is densest, 

 and the whole mass becomes enveloped in a membrane. Later on. 

 those cells in which polyhedral crystals are developing exhibit striations 



* Bull. Torrey Bot. Club, xl. (1913) pp. 555-65 (2 pis.). 

 t Comptes Rendus, clvi. (1913) pp. 1275-7. 



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