Increase in Variability in One Direction. 15 



be waited for. This is most forcibly brought out by the 

 fact that numerous horticuhural varieties are still at 

 exactly the same level as they were at the time of their 

 introduction. The most vigorous selection continued over 

 long periods of time has only rarely succeeded in effecting 

 a further improvement in the same direction. We are 

 familiar with hosts of variegated plants, but A urea vari- 

 eties are very rare. Flowers with petalomany are sterile, 

 and the plants can only be multiplied by vegetative meth- 

 ods. But it is quite clear that this difficulty is by no means 

 the cause of their rarity. Amongst composites we occa- 

 sionally find isolated heads without tongue florets, but 

 how small is the number of discoid varieties. I once 

 found an example of Coreopsis tinctoria in my cultures, 

 which exhibited only some spare ray florets, but although 

 I isolated the plant, the abnormality did not reappear 

 from its seed. CatacoroUa (an outward doubling of the 

 corolla so as to form lappets) occurs almost only as a 

 commercial race in Gloxinia superha. Fistulous compo- 

 sites are rare; there is room on the market for monoph- 

 yllous and laciniate varieties of many species, if only we 

 could make them. But so long as chance does not put 

 them into our hands, all our labor is in vain. 



Nevertheless, all plants no doubt possess numerous 

 latent characters. Any culture carried out on a sufficiently 

 large scale, or continued for several years, will give con- 

 vincing proof. In fact it is often very difficult to keep 

 races free from anomalies. Agrosteninia Githago, Raph- 

 anus Rhaphanistrmn and many other species contain an 

 almost inconceivable number. Amongst garden plants 

 desirable novelties must obviously be rare now because 

 they must have been already found and put on the market; 



