'85$ REPORT— 1903. 



peculiar interest. Their study has not as yet given any very reliable cluei to its 

 phylogenetic history. 



These phenomena show no line of demarcation between monocotyledons and 

 dicotyledons, but where differences exist between the ArchichlamydeEe and the 

 Sympetalse, monocotyledons are connected in these particiUars with the Archi- 

 chlamydese. 



2. On Stimulus and Mechanism as Factors of Organisation. 

 By Professor Farmer, F.R.S. 



3. Alternation of Generations in the Dictyotacete and the Cytology of the 

 Asexual Generation. By J. Lloyd Williams. 



1. The nuclei of the vegetative cells of tetrasporic plants have about thirty -two 

 chromosomes in the karyokinetic figure. 



2. In the stalk-cell division of the tetrasporangium the curved split chromo- 

 somes are easily counted and the unreduced number obtains. 



3. In the tetraspore mother-cell there is a long period of preparation for 

 division. A well-marked synaptic stage appears while the cell is still young and 

 small. The thread is distinctly polarised and the nucleolus very irregular in form 

 and frequently attached to the spirem. At this stage also, and at no other, the 

 nucleus has a small deeply staining spherule. After a time the thread becomes 

 thicker and less deeply stained, and it ultimately splits longitudinally. No clear 

 evidence has been seen of a second split — probably the .separating halves become 

 greatly alveolated and connected together by cross-threads so as to present the 

 appearance of the ordinary reticulum of the resting stage. This condition, during 

 which the identity of the chromatin thread is completely lost, persists for a long 

 time. Thick cloudy masses then appear, which gradually condense into sixteen 

 chromosomes. These are bent upon themselves until the limbs are parallel, or 

 cross each other, or form open rings. 



The ensuing division is distinctly heterotype, and the spindle intra-nuclear. 



4. The two daughter-nuclei in division have their axes parallel and the 

 spindles are formed on the sides of the nuclei remote from each other. The 

 division is homotype and the chromosomes show the reduced number. 



5. In the germinating spore the chromosomes have been counted in the 

 prophase, the equatorial plate, and the dispirem stages, and the number is always 

 sixteen. 



6. In the sexual plants, the dividing nuclei of the vegetative, antheridial, and 

 oogouial cells are characterised by having the reduced number of chromosomes. 



7. The curious abnormal figures found in unfertilised eggs show sixteen 

 chromosomes, while the dividing nuclei of the germinating oospores always have 

 the full number. 



The cytological evidence then shows that the germinating tetraspore grows 

 into a sexual plant, while the oospore on the other hand produces the tetrasporic 

 generation. Furthermore, the reduction stage has all the distinguishing characters 

 of the corresponding stage in the higher plants. 



TUESDAY, SEPTEMBER 15. 

 The following Papers were read : — 



1. Modern Views on the Phylogeny o/theAlgse. 

 By Dr. F. F. Blackman. 



