84 Varietfiten, Descendenz, Hybriden. 



The author's Interpretation is that one parent has the Constitu- 

 tion AA bb and the other aa BB, albinism being a double recessive. 



N*^ 13 indicates that the viability of the white seeds decreases 

 much more rapidly than that of the green seeds with age. 



The above conclusions are supported by evidence from other 

 Grosses. 



IL The author considers that the different parts of the plants 

 may possess different genetic constitutions. This conclusion isfounded 

 upon three chief series of facts. (a) In other crosses of groundsel 

 segregates the ratios of green plants to white plants varied widely 

 from the theoretical ratios of 3 : 1 and 15: 1. (b) Seeds from dijEferent 

 parts of the same plant may serve different results. (c) There is occa- 

 sionally found, growing wild, an isolated, variegated plant of groundsel 

 having more or less „mottled" leaves. 



A plant of this sort was transferred to the garden and not sel- 

 fed but seed collected from the whitest parts which were splashed 

 however with green. Most seedlings were white or yellow green and 

 perished in a week or so. There were also a few green and yellow 

 green seedlings, more or less variegated, which were picked out 

 and survived. The inheritance was not foUowed further however. 



The author's conclusion is that much more work is necessary 

 before a coherent account can be given of albinism. 



W. Neilson Jones. 



Trow, A. H., On the number of nodes and their distri- 

 bution along the main axis in Senecio vulgaris and i t s 

 segregates. (Journ. of Genetics VI. p. 1—63. 1916.) 



This paper deals with the genetic treatment ot the habit indi- 

 cated in the title. Node counting commenced in 1907 and has been 

 continued to the present time. Eleven different types originally 

 found wild and three radiate types bred from these by crossing have 

 been maintained pure for some years. 



Some of these were occasionally tested by exposing to different 

 conditions e. g. by growing some in sand}^ and some in clayey soil. 

 Such treatment however produced no transgressive variability in 

 the types. 



The author considers his results show that the nodal number 

 is the resultant of the interaction of a number of factors and is 

 governed in the flrst place directl}^ by these factors. 



Radiate and hairy types have higher nodal numbers than non- 

 radiate and glabrous types, there being distinct evidence ofcoupling. 



In the various pure families investigated, the nodal number 

 belongs to one of three main groups: low (9 — 15), medium (20 — 26) 

 or high (29—37). In the latter there appears to be a sub-group, also 

 in which the number is very high. The factors for rays and hair 

 and perhaps other factors, also, influence nodal number but not so 

 as to completely obscure the primär}'' three-fold Classification. 



The hypothesis put forward to account for the results of crossing 

 types with different nodal numbers is that two factors A and B 

 are concerned such that low (L)=:aaBB, medium (M)=AABB, 

 high (H) = AAbb. 



The results show that F^ from HXL,HXM,LXMandMXL = M 

 also L X L = L only (2 crosses made). 



MXM:=M only (1 cross made). 



L X M = Fl all M : F2 bimodal, and being recessive to M (3 

 crosses made). 



