190 SECTIONAL ADDRESSES. 
or apogamy, .or even to pathological conditions. A closer study of 
the living plants, and particularly the many discoveries of Sauvageau, 
together with careful cytological researches, and the consequent 
demonstration, in most of the groups examined, of meiosis, has greatly 
clarified our ideas regarding reproduction in the Brown Seaweeds, and 
made necessary a re-classification of some of the genera. 
In her interesting paper on Pylaiella, Dr. Knight! shows that the 
plants are either diploid or haploid, the former being the more numerous. 
Diploid plants may bear both unilocular and multilocular sporangia. 
The former undergo meiosis and consequently produce haploid spores 
which, as would be expected, germinate into haploid plants. The latter 
bear multilocular sporangia with haploid spores which fuse in pairs, and 
consequently are true gametes, and from the zygotes diploid plants again 
result. Returning to the plurilocular sporangia born on the diploid 
plants, the spores not having undergone reduction do not fuse, and 
consequently grow up into diploid plants, and in this manner there may 
be several successive generations of diploid plants. There is a further 
irregularity upon which fresh light would be welcome : in some cases the 
diploid number continues to the fourth or fifth segmentation of the 
sporange, and then, without any sign of synapsis, the number changes to 
the half. If the author (following Kuckuck) is correct in regarding 
Pylaiella as primitive, it is interesting to compare the fluctuating character 
of the cytological rhythm here with its firm stabilisation in Dictyota. 
There, out of many thousands of sexual plants examined, I have never 
seen a single one that bore tetra-sporangia"; nor have I seen more than 
one example where both oogonia and antheridia occurred together. 
There have been material additions to our knowledge of the repro- 
ductive organs of the Phzosporales, but there are gaps still to be -filled, 
and it is unfortunate that some supposed discoveries are received with 
doubt by some other investigators, who suggest that the reproductive 
structures observed belong to other plants growing epiphytically upon 
the ones described. 
Sauvageau’s account of the parasitic Hctocarpus Padine with its mega- 
and meio-sporangia, and its useless ‘ antheridia ’ is particularly intriguing. 
His description of reproduction in Dictyosiphon introduces us to a new 
type of alternation of generations, and it has already induced Taylor™ to 
institute a new sub-order to receiveit. It is interesting to note, however, 
that work done on plants growing on the Welsh coast give materially 
different results. There is no need to dwell upon Cutleria, for its interest- 
ing story is familiar to us. Clearly, one of the urgent problems in this 
field is the working out of the full life-histories and the satisfactory solution 
of the cytology of typical members of all the important genera of the 
Pheosporales. 
Let us now turn our attention to the Cyclosporales. Of the Dictyotacee, 
Haliseris (the three forms) and Taonia (tetrasporic plants) have been 
investigated by the writer; Georgevitch!® has examined the asexual 
10 Trans. Roy. Soc. Edin., 1923. 
11 It is true that a supposed case has been reported. In all probability, however, 
this was due to oospores segmenting on the thallus—a frequent occurrence. 
12 Bot. Gaz., 74, 1922. 
18 Comp. Rend. Acad. Sci., 167, 1918. 
