74 EIGHTEENTH REPORT. 



which the mycelium becomes bi nucleate is very variable. lu some 

 species the single nucleus of the basidiospore divides, so that from 

 that point on every cell of the mycelium is biuucleate, the nuclear 

 union taking place in the basidium, to be folloAved immediately 

 by reduction division so that the nuclei of the usually lour basidio- 

 spores are haploid. In other cases, however, the basidiospores re- 

 main uninucleate and the vegetative mj^celium possess but one 

 nucleus to the cell. Somewhere, however, before the hj'menium is 

 formed the cells become binucleate, apparently by the omission of 

 a septum after nuclear division, rather then by a true union. This 

 is so variable that I have had to indicate (Fig. 12) by a dotted line 

 the fact that the point where the cells become binucleate (and 

 which correspond to the i)oint of cell union) is not tixed. 



Reviewing now the different sexual cycles that have been illus- 

 trated, it will be noted that they all agree in the order of their 

 events, i. e., cell union, nuclear union and reduction division. But 

 these events are seen to be like movable balls on a wire ring. They 

 can be arranged in almost any j)osition, in close proximity by 

 threes or by twos or scattered, but they cannot be passed by one 

 another. Thus we have them in threes in the three possible com- 

 binations: liD, CU, NU in Fucus, CU, NU, ED in Ulothrix and 

 Oedogonium, NU, ED, CU, in Tilletia ; or by twos with the third 

 removed to some more distant point in the cycle as CU, NU in 

 Floridae and Mosses, NU, ED in Ascomyceteae and many other 

 fungi. The arrangement with all three items scattered evenly on 

 the cycle is, however, not known. 



We may for a little consider the bearing of the foregoing upon 

 alternation of generations as well as the effect of apogamy or 

 parthenogenesis upon the cycle. 



Strasburger was very insistent that the sporophj'^te always began 

 with the zygote and the gametophyte with the haploid cells pro- 

 duced in the course of reduction division, and refused to consider 

 as homologous two structures of similar morphological origin if 

 one contained ha])loid and the other diploid nuclei. Thus the car- 

 pospores of Nemalion are, following Strasburger, considered by 

 some as entirely lacking homology with those of Polysiphonia, in 

 spite of the fact that they are produced in the same manner, 

 moroi)hologically. The plant body of Fucus is called b}'^ such 

 botanists a sporophyte in spite of the fact that it bears the an- 

 therids and oogone. Is this right? 1 believe not. 



It is in the determination of this question that the cytological 

 studies of apogamous plants have thrown much light. Take the 



