SEXUALITY IN PLANTS—JOHNSON. 403 
that in the ascus. Claussen (1907) and Brown (1909) could find no 
other in the varieties of Pyronema studied by them. Both workers 
find paired nuclei associated in the ascogenous hyphe and finally in 
the young ascus. Claussen therefore regards the fusion in the young 
ascus as a union of descendants of the sexual nuclei that were brought 
together in the odgonium but did not fuse there. In other words, he 
thinks it a real sexual fusion which has been deferred.’ Brown, on 
the other hand, says that in his plant no antheridial nuclei are con- 
cerned, since the antheridium never reaches the odgonium. He 
therefore regards the fusion of pairs of nuclei, derived from the 
odgonium, which occurs in the ascus, as one that serves as a substitute 
for the sexual fusion that primitively occurred in the odgonium. 
Brown’s view is supported further by his work on Lachnea (1911), 
and by Faull’s recent work (1912) on certain Laboulbenias. 
If this view of Brown’s be accepted it implies that the original 
diploid condition of the cells of the sporophyte has been altogether 
eliminated, except for the brief uninucleate stage of the ascus. In 
spite of this, however, the whole structure and development of the 
original 2X generation, from fertilized odgonium to mature fruit 
and ascus, has been retained. This same normal type of vegetative 
structure, in spite of an abnormal chromosome number, has been 
demonstrated in gametophyte and sporophyte of aposporous and 
apogamous mosses and ferns. It is implied also in Lewis’s suggestion 
that, in the red seaweeds, the reduction has been postponed from its 
original jocation at carpospore-formation over into the primitively 
haploid tetrasporic phase of the next generation. 
Still other recent work on the Ascomycetes, however, supports 
Harper’s view that a double fusion frequently occurs in these fungi. 
Thus Blackman and Fraser (1906), Fraser (1907-8), and Fraser and 
Brooks (1909) find evidence of several steps in the loss of function of 
the antheridia in the different species of the cup fungi Lachnea and 
Humaria. In those cases where no antheridial nuclei are discharged 
into the odgonium, nuclei of this organ itself are believed, by these 
workers, to fuse in pairs within it. The later fusion in the ascus, 
which they find in common with all workers, they regard as a 
nutritive phenomenon. 
Until toward the end of last century the Basidiomycetes were 
generally assumed not to be sexual. At least no sexual organs had 
been described for them, with the exception of the spermagonia and 
ecidia of the plant rusts. These had been called male and female 
organs, respectively, by Meyen, before the middle of the century. 
_ The very first nuclear studies of the rusts and toadstools, however, 
revealed the occurrence of a nuclear fusion, and at another point in 
the life history indications of the complementary process, a reduc- 
tion, were discovered. 
