198 BOTANY 



description of these figures see Bagchee for the ascomycete, 

 Pustularia holarioides and Carter for Padina Pavonia. 



In the ascomycetes, three nuclear divisions occur in the ascus, 

 leading to the formation of eight daughter nuclei, which form the 

 nuclei of the ascospores. The centrosome in these forms is often 

 discoid in shape and lies against the nuclear membrane. With the 

 onset of mitosis, the aster develops in the cj^toplasm above the 

 centrosome, and the latter now divides to form two daughter 

 centrosomes. As the daughter centrosomes move apart, the 

 fibres of the intranuclear spindle can be seen projecting into the 

 nucleus. When the centrosomes reach the opposite sides of the 

 nucleus, the two groups of fibres become arranged in the form of a 

 sharp-poled spindle stretching across the nucleus with the chromo- 

 somes arranged at the equator. As a general rule, the nuclear 

 membrane remains intact until the chromosomes approach the 

 poles of the spindle at anaphase, when it may disappear and the 

 nucleolus escapes into the cytoplasm. There is thus no doubt that 

 in these forms the achromatic figure is of nuclear origin. 



The origin of the achromatic figure in the higher plants has led 

 to a good deal of controversy. On the older view special substances 

 were postulated in the cell to account for the origin of the figure. 

 Nothnagel advanced the view that exosmosis of the karyolymph 

 through the nuclear membrane into the cytoplasm caused precipi- 

 tation of the fine fibrils which compose the figure. This view has 

 been upheld by Tischler, who also suggested that intranuclear 

 figures are formed in the same way, except that it occurs here 

 through the inward diffusion of cytoplasmic fluid. 



The view that the achromatic figure is entirely nuclear in origin 

 has come to the fore within recent years from the investigations 

 of Devise and Robyns. Devise considered that the figure was 

 solely nuclear in origin in the sporocyte of Larix. It would 

 seem that the karyolymph becomes altered in some way by the 

 cytoplasmic fluid after the shrinkage and disappearance of the 

 nuclear membrane. 



Robyns has conducted a more elaborate investigation of the 

 problem of the origin of the achromatic figure. The plants 

 principally used were Vicia faba and Hyacinthus orientalis. For 



