ZOOLOGY AND BOTANYj MICROSCOPY, ETC. 105 



Polymorphism of the Phycochromaceae.* — W. Zopf details the 

 structure and development of a low algal form which he calls Tolypo- 

 thrix amphibia, and which he regards as confirming his view already 

 published as to the genetic connection of low forms of fungi. It was 

 found among the protonema of a moss, and had two forms, an aquatic 

 form, and an aerial form growing on the surface of water. The 

 aquatic form is filiform, and closely allied to the organisms which 

 make up the genus Tolypothrix. It consists of an unbranched filament 

 of cells inclosed in an evident sheath ; within this sheath it breaks 

 up into fragments or hormogonia. The aerial or chroococcus form 

 developes from hormogonia, consisting of three or more cells which 

 reach the surface of the water. Here a number collect together, 

 and their extremely thin gelatinous envelope coalesces together into 

 a continuous oily membrane. The blue-green colour of the hormo- 

 gonia has now passed over into a greener tint. In this condition the 

 cells divide in all three directions, and not in one only, as had pre- 

 viously been thought to be exclusively the case with the Scytonemese. 



Reproduction of Ulva.t — A. Borzi thus describes the develop- 

 ment and conjugation of the zoospores of Ulva Lactuca, which takes 

 place freely in cultivation. The zoospores are oval, and are provided 

 on the anterior beak with two colourless cilia, and, attaching them- 

 selves to one another by their anterior ends, coalesce in the course of 

 about five minutes into a swarm-spore twice as large with four cilia. 

 Occasionally the position of one of the conjugating swarm-spores is 

 reversed. Compared with the great number of swarm-spores, con- 

 jugation takes place very rarely, which may be the result of a sexual 

 differentiation, although none is visible externally ; there is no 

 difierence in their motility. Warmth influences favourably their 

 emission and motility. But it is interesting that while the ordinary 

 zoospores display distinct positive heliotropism, the zygospores acquire 

 an opposite heliophobic tendency, in consequence of which they seek 

 dark spots, where their further development may proceed. 



The zygospores lose their cilia and coalesce completely into an 

 oval body, in which the anterior end is still distinguished by the 

 absence of endochrome, while the other end has a great quantity of 

 chlorophyll and the two pigment-spots and starch-grains of the two 

 original zoospores. The zygospore attaches itself by its anterior end, 

 and, after growing rapidly, divides transversely. The basal and 

 apical cells finally become completely separated, this being preceded 

 by the apical cell becoming narrowed and prolonged at the base into 

 a beak-like colourless appendage. Similar transverse divisions follow, 

 and thus a small colony is formed of unicellular individuals closely 

 associated together, and constituting an asexual generation. Each of 

 these individuals developes into a new frond ; first of all becoming 

 attached by its colourless end, and then dividing first into a filament 

 and then into a plate of cells. 



* Ber. Deutsch. Bot. Gesell., i. (1883) pp. 319-24 (1 pL). Of. this Journal, iii. 

 (1883) p. 688. 



t Borzi, A., 'StuJi Algologici,' 117 pp. (9 pis.) Messina, 18S3. 



