No. 463.] STUDIES ON PLANT CELL. VI. 469 



zygospores of Conjugates on germinating present similar events. 

 The teleutospore and basidium are probably also the seat of 

 chromatin reduction (Blackman. : O4b) in the formation of 

 spores either directly or through the promycelium. The ascus 

 holds a position at the end of a sporophyte phase which suggests 

 a similar relation in this group of fungi. Chromosome reduction 

 may also be expected in the tetraspore mother-cell of the Rho- 

 dophyceae, as in Dictyota, but this subject has never been inves- 

 tigated. There are occasional red algae in which the tetraspores 

 are sometimes borne on the same plant with the sexual organs, 

 conditions which may be difficult to explain on the theory that 

 the tetrasporic plant is a sporophyte. Thus Spermotliainnion 

 turneri on the American coast frequently bears both procarps 

 and tetraspores on the same plant, and I have also seen cysto- 

 carpic plants of Ceramium rubrum some of whose branches con- 

 tained tetraspores. Lotsy (: O4a) also reports similar conditions 

 in Chylocladia kaliformis. The other extremely varied methods 

 of spore formation (zoospores, conidia, etc.) in the thallophytes 

 do not concern the present discussion. They seem to have no 

 fixed place in the life history and there is nothing to indicate 

 any relation to reduction phenomena, although we actually know 

 nothing about the chromosome history among these lowly forms. 

 The importance of sporogenesis as a critical period in the life 

 history of higher plants became at once apparent with the dis- 

 covery that fertilization doubled the number of chromosomes in 

 the nuclei of the sporophyte phase and that the double number 

 was reduced during sporogenesis. As stated in our account of 

 gametogenesis, these facts were first established for a number of 

 spermatophytes by the work of Strasburger ('84, '88, and '94), 

 Guignard ('84, '85, and '91), and Overton ('93 a and b). Guig- 

 nard ('91) presented for Lilinm martagon the first complete 

 account of the number of chromosomes in the life history of a 

 plant, and his results were also established independently by 

 Overton ('93 a and b). Then followed confirmatory investiga- 

 tions among the bryophytes in the work of Farmer ('94, '95 a, 

 b, c) and in the pteridophytes by Strasburger ('94, p. 294) for 

 Osmunda. Since 1895 the investigations among the spermato- 

 phytes have so multiplied that we know the number of chromo- 



