214 SUMMARY OF CURRENT RESEARCHES RELATING TO 



known. S. Harveyana Sauv. is regarded as the southern homologue 

 of S. Hystrix. The author re-establishes S. bipinnata Kiitz., a parasite 

 of Halidrys siliquosa and Gystoseira fibrosa. This species bears numerous 

 unilocular sporangia, but the propagula are very rare. Plurilocular 

 sporangia of one size only occur. S. fusca is also revived as an inde- 

 pendent species. The only reproductive organs hitherto known for this 

 plant are trif urcated propagula bearing cylindrical or gradually attenuated 

 rays. The real S. cirrosa is very variable as regards its propagula, and 

 as a result of prolonged study the author divides the forms into septen- 

 trionalis, meridionalis, and mediterranean Between these forms are, of 

 course, many intermediate ones, but the extremes are markedly cha- 

 racteristic. The author describes the chief points, and gives the general 

 distribution of each of the three forms. The paper closes with some 

 interesting remarks concerning the modes of reproduction in the specie3 

 mentioned. Those species which are parasitic show much more per- 

 fectly developed organs of , reproduction than those which are inde- 

 pendent and free. For example, S. Hystrix and S. furciyera, two 

 parasitic species, possess well-developed plurilocular sporangia of two 

 kinds, probably oogonia and antheridia ; and S. bipinnata, also a para- 

 site, has plurilocular sporangia of one kind pointing to the possibility 

 of isogamy, while its propagula are very rare. On the other hand, 

 S. cirrosa, a free plant, appears to have lost its sexual reproduction and 

 multiplies by means of propagula, and so far as is known of S. fusca 

 the same facts hold good. The difference between the effect of para- 

 sitism on Sphacelaria and on the higher plants is remarkable : in the 

 former case it acts as a stimulant, in the latter it leads to degeneration. 



Kelps of Juan de Fuca.* — C. McMillan gives a general account of 

 the LaminariaceEe of this region. Seventeen out of the twenty-five 

 genera of this order are represented in the Straits of Fuca, and of 

 many of them the author has made a special study. His results are 

 presented here in a more or less generalised form, and the paper closes 

 with a description of the external characteristics of each genus. 



Alternation of Generations in the Dictyotacese.f — L.Williams 

 gives a short abstract of a paper which is to appear in full in the 

 Annals of Botany. In this group the asexual cells are borne on plants 

 distinct from those that bear the sexual cells. Cytological evidence 

 has been obtained showing that the cells of the tetraspore-bearing 

 plants contain twice as many chromosomes as those of the sexual plants. 

 The mother-cell of the four tetraspores shows synapsis, has all the 

 characters of a heterotype division and shows sixteen chromosomes. 

 In the male plant of Dictyota the reduced number is present in all the 

 divisions of the antheridium, and in the female plant the division 

 which cuts off the stalk-cell of the oogonium also shows the reduced 

 number. The fertilised egg-cells show, naturally, the double number. 

 There is thus complete cytological evidence for the alternation of 

 gametophyte and sporophyte, though experimental cultivation from 

 spore to spore has hitherto been unsuccessful. 



* Postelsia, 1902, pp. 195-220 (5 pis.). 

 t New Phytologist, ii. (1903) pp. 184-6. 



