18 



THE AMERICAN NATURALIST 



[Vol. LV 



from the type parent are left behind in the lower parts. 

 Such a case may perhaps be compared with the condition 

 seen in the variegated Spircea, and we may fairly con- 

 jecture that, if it were possible to raise root-cuttings 

 from the peas, they would produce types. 



A more gradual exclusion of the type-elements in the 

 lower parts is seen in certain intermediates. Thes^ may 

 scarcely differ from types in the lower parts, though 

 changing to rogues, sometimes abruptly, sometimes 

 gradually, as the series of flowering nodes is developed. 

 Eeciprocal crosses between the successive flowers of such 

 plants and the flowers of types has shown that, together 

 with the gradational change in the somatic structures, 

 there is also a gradational change in the proportion of 

 gametes bearing the rogue and type characters respec- 

 tively. This proportion and the rapidity of the change 

 differ on the male and female sides. Of the egg cells 

 ill the lower flowers, up to about the tenth flowering node, 

 rather more than 50 per cent, carry the type-characters 

 — or at least the non-pointed leaflets — but above this 

 level the proportion of types declines. Of the pollen in 

 the lowest two flowers only about 20 per cent, is type- 

 bearing and the proportion diminishes rapidly in each 

 successive flower above the level. 



In all the examples given hitherto the segregation is 

 in diploid tissues, but a comparable phenomenon has 

 been proved by Collins to occur in the haploid axis of a 

 moss (Fiinaria). In a dioecious moss, as the Marchals 

 have shown, sex-segregation occurs at spore-formation, 

 the division in which reduction is effected. This, of 

 course, agrees with cytological expectation, though, so 

 far as I know, the details have not been observed. But 

 from the leaves of mosses placed in nutrient fluids new 

 plants may be raised without great difiiculty, and Collins 

 found that the (perigonial) leaves surrounding the male 

 organ thus propagated, produce exclusively male axos.^^ 

 He has since raised similar cultures from the (peri- 

 ls jo«r. Gen., Vol. 8, p. 145 (1918-19). 



