278 DR. J. W. HESLOP HARRISON ON 



These facts support, to some extent, Rosenberg's conception 

 of the linking of apogamy and high chromosome number but 

 nullify the attempt to correlate apogamy and tetraploidy qua 

 tetraploidy — at any rate in this genus ; for within its limits 

 we have on the one hand the tetraploid* Phiipinellifolice 

 mi'crogenes pollinated normally, and on the other the tctraploid 

 ViUoscn apomicticaL Except by analogy, since none of the 

 British Roscc are octoploid species, their evidence neither 

 confirms nor confutes tlie possible relation which Gates, on the 

 basis of Strassburgers work, draws between octoploidy and 

 apogamy in Eualcheinilla. 



Returning now to the dependence of apomixis on hybridity, 

 let us attempt to discover how the latter can induce the 

 former. Since the supersection Ca/iince and the allied Svn- 

 styhe include both sexual and apomictical microgenes, and 

 further since the former is the more primitive and normal state 

 in the Rosacea;, it is a reasonable assumption to make that the 

 apomictical roses are derived from the sexual types. Moreover, 

 it seems a fair deduction from the foregoing work to regard 

 many rose microgenes as latent hybrids. If they are hybrids 

 they can be between forms whose physiological divergence is 

 slight or between forms where it is great. Suppose a cross of 

 the second type to take place. Arguing from the analogy of 

 the Liiiaria hybrids, or, appealing to the animal world, of the 

 two Oporahia dihifafa-aiitiiinnafa hybrids in which in the 

 reduction division few or no chromosomes find partners, we 

 may anticipate similar happenings in the Fi generation of our 

 wide rose cross. Hence, in the pollen formed, in place of the 

 reduced number of chromosomes we have the full somatic 

 number. This pollen, again, if the power of the Linaria 

 pollen or of the aiitiimiiala-dilufata spermatozoa is any 

 criterion, will be defective and therefore impotent —deficiencies 

 leading to its collapse. In the same way, in megaspore 

 formation we have a similar failure of redaction, so that when 

 the egg nucleus appears finally, even prior to fertilisation, it 



^i.e. if we regard the haploid chromosome number of seven encountered 

 ill l\, arvinsis and R, ni^^osix as the base. 



