VOLUME XXXII NUMBER 3 
DOLANIGAL. (ter LE 
SEPTEMBER, ro0r 
GAMETOGENESIS AND FERTILIZATION IN ALBUGO. 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY. 
XXIX. 
FRANK LINCOLN STEVENS. 
(WITH PLATES I-IV) 
[Continued from p. 98.] 
Il. PHYLOGENETIC. 
Tuis study of Albugo has established a series of forms 
showing advances in certain respects and a marked reduction in 
others. The species are closely related, and the difference 
between two consecutive members of the series is not great, 
although the extremes are widely divergent. There are four 
prominent structures or conditions connected with the series, 
namely, the coenocentrum, the receptive papilla, the mode of 
zonation, and the number of functional nuclei. Arranged in the 
order of these characters the species may be listed as A. Portu- 
lacae, A. Bliti, A. Tragopogonis, and A. candida. In this series 
the coenocentrum constantly increases in complexity of structure 
and perfection of function, the receptive papilla becomes less 
conspicuous, the number of functional nuclei decreases, and the 
mode of zonation varies in the last two species. These condi- 
tions are graphically represented in the accompanying figure 
which is self explanatory. We may consider the series as a 
possible expression of the phylogeny of the genus. Which 
conditions are likely to be primitive ? 
157 
