1904] _DAVIS—SEXUAL ORGANS IN PLANTS 259 
The old group of the Oomycetes has been a favorite starting point 
for evolutionary lines in the Ascomycetes and Mucorales. DEBARY 
pointed out the resemblances between the Ascomycetes and members 
of the Peronosporales, and since his time a number of writers have - 
traced lines of relationship with greater or less detail. The most 
recent expression, that of BARKER (’03), considers Albugo as presenting 
sexual organs sufficiently primitive to be like the progenitors of the 
Ascomycetes. The less complicated sexual organs of Gymnoascus, 
Eremascus, etc., and the similar conditions in the Mucorales have 
very generally been regarded as derived from higher conditions (as 
in Albugo) by a process of simplification or degeneration, whereby 
sexually different gametes become essentially similar. 
The two regions of the algae most discussed in attempts to establish 
points of origin of the higher Phycomycetes and Ascomycetes have 
been Vaucheria and the Rhodophyceae. The resemblances of Vau- 
cheria to the Peronosporales and Saprolegniales are very striking, the 
more so since the recent studies in oogenesis have brought all groups 
= close sympathy. The author believes that that there are relation- 
ships here, although probably they are not direct. But when the 
Mucorales are annexed on the theory that the highly differentiated 
Sexual organs of heterogamous groups may become generalized to 
those of the molds, then difficulties appear which seem at present 
msurmountable. There is no morphological evidence of such a line 
* development, and the Process as a physiological event would be 
quite unparalleled and contrary to all known principles of sexual evo- 
ray And: similarly Barker’s view that Albugo Bliti presents 
at conditions simple enough for the most primitive ascomycete 
ar ag to the author justified by its cell and nuclear activities 
The Rage see 
Shidies able resemblances between the Laboulbeniaceae and 
ae ey ag have been noted by THAXTER ( '96), who has sug- 
t kined : Ee ettes may have arisen from this point in the 
Mg cei The similarity of the Laboulbeniaceae to the red 
very striking, and there are no more interesting 
ne region of plant morphology than those involving 
—. of the sexual processes and the development 
"PB 4Nd ascocarp in these two groups. There are indica- 
Of the 
