8 THE COTTON PLANT IN EGYPT CHAP. 



into hollow cones. These unite laterally to form the 2- 

 to 6-locular ovary, while the combined apices of the cones 

 elongate to form the style (sy.). Large-celled conducting 

 tissue is formed at the base of the style and in the radial 

 walls, which afterwards facilitates transit for the burrowing 

 pollen-tube. On the inner side of these hollow cones 

 (y. ov.) there arise the ovules with their double integu- 

 ments ; a single cell in the centre of the nucellus enlarges 

 into the single megaspore mother-cell. 



The microspore mother-cells are formed in plates below 

 the epidermis of the embryo anthers (st.) on the staminal 

 column. They arise from the cell-layer immediately 

 below the epidermis, but soon separate themselves from 

 it by two layers of cells, and then enlarge till their 

 diameter is about 40 //, when they pass into the synapsis 

 stage. Meanwhile (Fig. 8), the cells which surround them 

 on all sides divide once, and thus give rise to a tapetum, 

 which is ultimately disintegrated. 



The mechanism of nuclear division in reduc- 

 tion. 28 This division has not been captured for observa- 

 tion in the megaspore mother-cell ; it appears to take place 

 very rapidly, judging by the ease with which the stages 

 immediately precedent and antecedent can be found. 

 The same applies to the microspore mother- cell, where 

 the stage is easily observed about ten days before the 

 flower is due to open. 



The extraordinary minuteness of the chromosomes of 

 Gossypium is very obvious in this division, where they are 

 inconspicuous in comparison with the linin threads, which 

 have actually been figured in error as the chromosomes 

 themselves. The latter appear to consist of twenty groups 

 of pseudo- tetrads, each unit of the group being about 

 0'6 fi in diameter, arranged in prophase along one side 

 of the somewhat tangled close spireme of linin. This 

 spireme splits longitudinally and the two halves separate 

 like loops of cotton in a broken soap-bubble, retaining 



