SEXUAL REPRODUCTION 89 



number of cases in which a nucleus was actually found 

 passing into the fertile cell from one of the smaller cells of 

 the mycelium at its base. The migrating nucleus passes 

 from a cell situated below the fertile cell, and sometimes 

 passes into the fertile cell immediately above it, or more 

 frequently passes into a fertile cell belonging to another 

 row, situated by its side. The migrating nucleus is reduced 

 to a thin thread during the process, and neither before nor 

 after its passage could a pit in the wall be observed. 

 Although two nuclei are usually eventually present in the 

 fertile cell, three are sometimes to be seen, in fact three 

 nuclei are nearly always to be found in a few of the fertile 

 cells of each aecidium. In one case a fertile cell containing 

 four nuclei was observed. Whether this number of nuclei 

 was due to the migration of more than one nucleus into 

 the fertile cell, or to division of the usual two nuclei, was 

 not determined. 



Fusion does not take place in the fertile cell between the 

 two or more nuclei present. These divide by what is 

 termed conjugate division, and when two nuclei are present 

 in the fertile cell, two nuclei are present in each aecidio- 

 spore, and three when the fertile cell contains three nuclei. 

 Nuclear fusion takes place at a later stage of development 

 between the pairs of nuclei found in the teleutospores. 



It is considered that throughout the group the aecidium 

 must be looked upon as a sorus of reduced female organs. 

 Considering the spermogonia and aecidia as male and 

 female reproductive organs respectively, it is evident that 

 those Uredineae which possess an aecidial stage exhibit 

 a well-marked alternation of generations. The sexual 

 generation spermatia and aecidia having single nuclei, 

 with two chromatin masses on division ; the asexual genera- 



