376 SUMMARY OF CURRENT RESEARCHES RELATING TO 



conjugation the fruiting and vegetative filaments all disappear. In 

 the laboratory Spirogyra fruits not at the surface but always near the 

 substratum ; in the field the reverse holds good. Conjugation is found 

 to result not so much from external as from internal conditions. Spiro- 

 gyra evidently has definite periods of growth and activity. 



Structure and Development of Martensia.* — N. Svedelius gives an 

 account of the structure and development of Martensia. Finding the 

 respective explanations by Harvey and Agardh as to the origin of the 

 reticulate zone of the thallus to be insufficient and in conflict, he has 

 investigated the matter for himself. He describes the true mode of 

 formation of the reticulum, the development of the tetraspores, of the 

 spermatia, and of the cystocarp. 1. He shows that the growth of the 

 frond from an early stage is carried out almost exclusively by means of 

 a characteristic intercalary cell-division which reaches its maximum in 

 the formation of the reticulum ; and that there are three types of this 

 mode of growth represented by M. fragilis, M. pavonia, and M. flabelli- 

 formis. 2. The tetrasporangia are borne on the lamella? of the reticulum 

 normally, but in some species may occur simultaneously on the basa- 

 disk. They are immersed ; and their unicellular rudiments have, like 

 the other cells of the plant, originally several nuclei each. These nuclei 

 increase in number to perhaps fifty in the cell, and then degenerate and 

 disappear — all but one, which, situated in the middle of the dense mass 

 of tetrasporangial protoplasm, divides into the four definitive tetraspore- 

 nuclei. 8. The spermatangia are borne only on the lamella? in one or 

 more sori on special male plants. They rise from superficial cells which 

 by repeated division are cut up into uninucleate mother-cells, which 

 then begin an apical growth and cut off one or two uninucleate 

 spermatangia. Schmitz's view, that the spermatangia in the Floridea? 

 are always apical cells of branches with apical growth, applies therefore 

 to Martensia despite its otherwise strong intercalary mode of growth. 

 The different modes of development shown by the spermatangium- 

 mother-cells and their various methods of cutting off spermatangia 

 afford important characters for distinguishing various types of organisa- 

 tion among the Floridea?, and have a systematic value. 4. The 

 cystocarps are borne exclusively along the edges of the lamella?. The 

 carpogoniuin is an apical cell on a special branch with apical growth (as 

 Schmitz has shown to be the case in the Floridea? always). All the cells 

 in the carpogonial branch and carpogoniuin are multinucleate. After 

 the fertilisation, the formation of the auxiliary cell and its division 

 into foot-cell and central-cell, the gonimoblast-threads arise from the 

 latter, and are all commonly uninucleate. They produce the carpospores, 

 which are also uninucleate only. 



Yellow-brown Cells of Convoluta paradoxal — F. Keeble has 

 studied the life-history of the accelous Turbellarian Convoluta paradoxa, 

 which haunts shore algae, and which is remarkable for containing 

 certain yellow-brown algal cells. These cells are indispensable to the 

 welfare of the animal : without them it dies. When starved it digests 

 them and becomes infected again. The alga multiplies rapidly in the 



* K. Svensk. Vet. Akad. Handl., xliii. No. 7 (1908) 101 pp. (i pis. and 62 figs.). 

 t Quart. Journ. Micr. Sci., Hi. (1908) pp. 431-79 (3 pis.). 



