28o DR. J. W, HESLOP HARRISON ON 



With dominance in the apomictical forms, and dominance 

 followed by segregation in the sexual microgenes, it is clear 

 that the notion of the species-t^'pe remains unaffected. 



l^olYeiiihrvoiiy. 



Linked up in some way with apomixis, and depending like 

 it on the presence of unreduced chromosome numbers in the 

 cells of the egg-apparatus, in many roses these cells, as well 

 as the egg-cell proper, 'develop into embryos. Thus Rosa 

 produces for our benefit a further complication, that of 

 polyembryony. Concerning this I caiuiot say more at this 

 juncture, for work in this direction is not complete. 



IV.— PIIENHYBRIDS OF ROSA. 



.So homogeneous in their traits are tlie various members ot 

 the supersection Canhne, and so delicately graded are the 

 relations between the sections, that only in exceptional cases 

 could intersectional hybrids be detected as such. If that is 

 true of such wide crosses as those between sections, then the 

 extreme difficulty of distinguishing hybrids of t^e various 

 microgenes within the same section by ordinary macroscopic 

 features v«ill be plain. Further, if hybridity between parents 

 so related does exist (and from what has been said previously 

 we know that it does), only pollen conditions under ordinary 

 circumstances will betray it. Nevertheless, even that criterion 

 will fail to gi\'e the faintest indication concerning the micro- 

 genes which gave rise to any given plant. Clearly then, this 

 chapter, which will deal with wild plants patently hybrid, 

 cannot in general include inter-Canine crosses ; still, as we 

 shall discover, two* such are brought forward, although their 

 recognition was due to exceptionally favourable conditions. 

 iVIoreover, since the work described here was carried out in 

 northern comities, wliere the only otlier section occurring in 

 quantity sufficient to give a reasonable prospect of hybridity 

 is the Fi/npine/lifolice, we have to consider, in the main, crosses 



* .Since this above was written Jebe of Christiana lias indicated severfi! 

 other similar hybrids. 



