216 BOTANY 



mediate position between the two schemes. The maintenance of 

 a reticulum throughout the post-synaptic stages and subsequent 

 formation of chromosomes on this reticulum structure, with omis- 

 sion of the pachynema stage, indicates a lowly type of nuclear 

 specialisation, which may perhaps be correlated with the parasitic 

 nature of the plant. The nuclear behaviour of Lathrcea suggests 

 that in the course of nuclear evolution some similar method of 

 chromosome formation may have existed, and that a specialised 

 spireme was evolved later with the consequent para- or telo- 

 synaptic pairing of the constituent chromosomes. 



Brachymeiosis. The nuclear life-cycle of the Ascomycetes has 

 for a number of years been a matter of acute dispute. The fusion 

 of two nuclei in the ascus was first observed by Dangeard many 

 years ago, and was considered by him to be a true sexual act. The 

 matter, however, soon became complicated when Harper, followed 

 by a number of investigators, claimed that a fusion also occurred 

 at an earlier stage in the life-cycle. This preliminary fusion was 

 stated to occur in the archicarp after the entrance of the male 

 nuclei from the antheridium. In those forms in which the anther- 

 idium was functionless, or even absent, the fusion of two female 

 nuclei (Humaria granulata, Blackman and Fraser), or even two 

 vegetative nuclei (Humaria rutilans, Fraser) was described. This 

 earlier fusion was then considered to be the true sex act and the 

 fusion in the ascus vegetative in nature. Following the fusion in 

 the ascus, there are three nuclear divisions in these forms, leading 

 to the production of eight daughter nuclei which form the nuclei 

 of the ascospores. The first division is heterotypic and the second 

 homotypic, and some years ago Fraser put forward the claim that 

 the third division was also a reducing division, and termed it a 

 " brachymeiotic " division. If there be two fusions in the life-cycle 

 of these forms it is clear that there must be two reducing divisions, 

 and Fraser was the first investigator to bring forward evidence 

 of such a second reduction. Following on this alleged second 

 reducing division, other workers in Fraser's laboratory also claimed 

 to have seen such a brachymeiotic division. 



The first opposition to such a view came from Claussen, working 

 with the discomycete Pyronema confluens. In an admirable paper 



