2S4 SANSOME 



D. M. Mottier(i9i i) mentions that there was no report of male 

 prothalli ever having been induced to become monoecious in the 

 fern Onoclea. In many species of fern with monoecious prothalH 

 the male organs develop first, and later, when there is a greater 

 supply of nourishment, archegonia are formed. In the hetero- 

 gametophytic Onoclea, however, female prothalli may form 

 male organs but male prothalli never form female organs. 



The regenerative experiments carried out on mosses by the 

 Marchals, Wettstein, Correns and Wilson show that in hetero- 

 thallic mosses, the environment rarely changes the sex expression 

 of a particular genotype. Wilson's experiment with Mnium 

 hornum, where he found an intersexual axis with the haploid 

 number of chromosomes, only indicates that the genetic deter- 

 mination may on occasion be interfered with by external 

 factors, but does not, as he suggests, vitiate the factorial theory 

 of sex determination for that species. 



Nagai (1919) found two hermaphrodites along with twenty 

 dioecious prothalli of Blechnum, Woodwardia and Adiantum. 

 The antheridia and archegonia were localised according to the 

 metabolic rate, the male organs occurring in the portions with 

 less available food supply than that of the portion bearing the 

 female organs. 



The rule holds that the female organs are situated in a 

 position of higher metabolic rate than the male organs. A 

 consideration of the secondary sexual characters (Goebel, 

 1 910), position of the gonads on the plant, and of the reactions 

 of the plant to external factors suggests this general principle. 



Various workers still advance the view that environmental 

 influences control the determination of sex in some plants. 

 They hold that the determination of male or female organs 

 depends upon the metabolic rate proceeding at the time of 

 gonad formation. It is, however, much more reasonable to 

 assume that genetic factors are the basis of the determination 

 of sex and that environment controls, in various degrees, the 

 expression of that determination. 



There is an increase in the stability of the expression of sex 

 as we pass from the lower to the higher plants, and at the same 

 time an increase in the potency of genetic determiners over that 

 of environmental factors. Also there is a concentration of genetic 

 factors towards the establishment of one fundamental or princi- 



