266 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tubes in Macrocystis and Ncrcocystis, in which the stem attains an enor- 

 mous length without any corresponding increase in thickness, and in a 

 weak climbing stem like Cucurbita ; while in the allied genus Lessonia, 

 which has a very stout and erect stem with long-continued secondary 

 growth in thickness, they are altogether wanting. 



Development of Confervacese.* — Ilerr G. Lagerheim has investigated 

 the life-history of Conferva bombycina and of some species of Microspora, 

 belonging to the Confervacea), under which family he includes the genera 

 Binuelearia, Chsetomorplia, Conferva, Hormiscia, Microspora, ffliizoclonium, 

 Ulothrix, and Ulospora. 



The cells of Conferva bombycina contain several small disc- shaped 

 parietal chromatophores without pyrenoids or starch, and a single 

 nucleus. From each cell may be produced either one or two zoospores ; 

 in the latter case the cell-contents are first divided in two by a colourless 

 septum of protoplasm ; the cuticle of the cell is converted into mucilage 

 before the escape of the zoospores. These are elongated ovate bodies 

 provided with a single small disc-shaped chromatophore and a single 

 cilium, but no red pigment-spot ; their movement is not dissimilar to 

 that of a Euglena. The young CW/er*;a-filarnent springing from it has 

 at first the appearance of a Characium. These correspond to the mega- 

 zoospores of Wille, two different kinds not having been observed in this 

 species. They very closely resemble the uniciliated megazoospores of 

 Botrydium. 



Eesting-cells are also formed in this species, either one, two, or four 

 proceeding from a single cell of the filament, by the cell-contents 

 rounding off, and inclosing themselves with a cell-wall while still within 

 the parent-cell. They correspond, therefore, to the aplanospores of 

 Wille. They hibernate within the dead cells of the parent-filament, and 

 germinate in the spring. Eesting swarm-cells are also formed in the 

 same way. These escape from the parent-cells without any cellulose- 

 coat, move about with an amoeboid motion, finally come to rest, and coat 

 themselves with a wall of cellulose. Whether these, on germination, 

 produce zoospores, has not been observed. 



The formation of the megazoospores of Microspora was observed in 

 M. Willeana n. sp. and stagnorum. The parent-cells contain several 

 ribbon-shaped chromatophores and starch, but no pyrenoids, and a single 

 nucleus. The zoospores are of two kinds. The megazoospores are pro- 

 duced either singly or two in each parent-cell, their size varying between 

 10 and 14: /x; they are biciliated ; they have no pigment-spot; the 

 chlorophyll is moderately uniformly distributed over the periphery, and 

 contains starch-grains. They appear to pass through a period of rest 

 before germinating. Megazoospores are occasionally produced with four 

 cilia ; they probably germinate in the same way. Kesting-spores and 

 resting swarm-spores of the same kind as those in Conferva bombycina 

 were also observed in M. Willeana. 



The author considers the above characters quite sufficient to keep 

 apart the genera Conferva and Microspora, though several species usually 

 placed under the former must be transferred to the latter genus. He 

 also regards them without doubt as fully developed algae, and not as 

 stages of development of higher alga3. 



* Ber. Deutsch. Bot. Gesell., v. (1887) pp. 409-17. 



