I have already mentioned that the rapid production of large numbers of new varieties, by [626] means of the crossing of the offspring of a single mutant with previously existing sorts, is a very common feature in horticultural practice. It warns us that only a small part of the novelties introduced yearly are due to real mutations. Further instances of novelties with such a common origin are the purple-leaved dahlias, the gooseberries without prickles, the double petunias, erect gloxinias and many others. Accumulation of characters, acquired in different races of a species, may easily be effected in this way; in fact it is one of the important factors in the breeding of horticultural novelties. I have alluded more than once in this lecture to the question, whether it is probable that mutations occur in one individual or in more. The common belief among horticulturists is that, as a rule, they appear in a single plant. This belief is so widespread that whenever a novelty is seen for the first time in two or more specimens it is at once suggested that it might have originated and been overlooked in a previous generation. Not caring to confess a lack of close observation, the number of mutants in such cases is usually kept secret. At least this statement has been made to me by some of the horticulturists at Erfurt, whom I visited some years ago in order to learn as much as [627] possible about the methods of production of their novelties. Hence it is simply impossible to decide the question on the basis of the experience of the breeders. Even in the case of the same novelty arising in sundry varieties of the same species, the question as to common origin, by means of crossing, is often hard to decide, as for instance in moss-roses and nectarines. On the other hand, instances are on record where the same novelty has appeared at different times, often at long intervals. Such is the case with the butterfly-cyclamen, a form with wide-spreading petals which originated in Martin's nursery in England. The first time it was seen it was thought to be of no value, and was thrown away, but when appearing for a second time it was multiplied and eventually placed on the market. Other varieties of _Cyclamen_, as for instance the crested forms, are also known to have originated repeatedly. In concluding this series of examples of horticultural mutations, I might mention two cases, which have occurred in my own experimental garden. The first refers to a tubular _Dahlia_. It has ray-florets, the ligules of which have their margins grown together so as to form tubes, with the outer surface corresponding to the pale under-surface of the corolla.