288 Non-Isolahle Races. 



ing easily produced by green plants and green branches 

 by variegated ones. 



Now let us consider the yellow seedlings of variegated 

 plants. They appear, it is true, to be mutants, but, as a 

 matter of fact, they are the extreme variants which, how- 

 ever, do not attain to their goal but perish in the attempt, 

 for tliey are too poor in chlorophyll and are thereby des- 

 tined to die early. Nearly all of them die without so 

 much as having unfolded their first leaves, or sometimes 

 even their cotyledons. They constitute the extreme limit 

 of a long series of variegated forms, but have, so to 

 speak, followed a wrong direction. They are by no 

 means rare ; for instance they are well known in the 

 holly. Ilex Aquifolhim, and they often result in a very 

 considerable loss amongst the seedlings raised from the 

 seed of variegated plants. 



It is not, however, variegated plants only which pro- 

 duce such seedlings; green plants do so only too often, 

 and this even occurs in families cultivated for experi- 

 mental purposes when the cultures are pure green and 

 have been so for many years or did not produce more 

 than an occasional variegated leaf or twig. If in such 

 cases the seeds of the single seed-parents are sown sepa- 

 rately the proportions in which variegated seedlings oc- 

 cur in the various groups are found to vary greatly. 



Some species appear never to produce them, for In- 

 stance the tricotylous races of Cannabis safk'a, Mcrcu- 

 rialis annua, and Pliacclia tanacetifolia which I have 

 cultivated, although I have sown the seeds of several 

 hundreds of individual plants separateh^ in the course of 

 some years. In other species they are very rare ; in some, 

 however, the percentage of yellow seedlings is so con- 

 siderable as to become a real nuisance. Thus, for in- 



