Bearing in mind, then, the principle that all cultivated hybrids should have a third part, cultivar-name, we can turn again to the use of the various possible designations for the second part listed above. The choice of designations depends, broadly speaking, on convenience, that is to say, on what, in practice, will be found the most useful method of referring to the plants concerned. In principle, of course, every hybrid whose parentage is known has an appropriate formula-designation, and in certain cases such a formula would be sufficient as a second part designation without inventing either a Latin name or a vernacular collective name. For instance, when there are only a very few forms of a particular cross, it might not be considered necessary to be able to refer to the forms collectively, and a second part name would not then be given. For example, Rubus 'Merton Thornless,' when raised, was the only form of the hybrid R. rusticanus inermis × thyrsiger to be put into circulation, and it was not given a second part designation other than the appropriate formula. On the whole, however, it is usually desirable to have a second part, collective designation, rather than a formula only. Whether such designation should be a Latin name or a vernacular phrase, or both, depends on a number of factors which, as I have said, are not yet fully worked out or appreciated. Broadly speaking, if there are a large number of cultivars of a particular cross and these cultivars form a well-marked group, distinct from other hybrid groups in the genus, it is useful to have a vernacular designation for general use, e.g. 'Bellingham Hybrids' for all cultivars of the cross Lilium Humboldtii × pardalinum. This purpose can, however, be equally well served by a Latin name, e.g. Camellia × Williamsii for all cultivars of the cross C. japonica × saluenensis. Whichever method is chosen, two points are of great importance. Firstly, if a Latin name is given, it must be accompanied by a Latin description. Secondly a vernacular designation must contain some such word as Hybrids, Crosses, or the like, to distinguish it from a cultivar-name. The practice, in some groups, of giving "straight" cultivar-names as second part collective designations, followed by "var. so-and-so," is condemned by the Code. Existing names of this kind, however, can easily be brought into line by adding a word such as Hybrids or Grex to the old, second part, cultivar-name, and omitting the "var." thus, Cattleya 'Fabia' var. 'Prince of Wales,' would become C. ('Fabia Grex') 'Prince of Wales' (Grex can he abbreviated to G. if desired). This alteration may seem over-pedantic, but if, in the naming of cultivated hybrids, a clear distinction is not kept between second and third part names, confusion, as I have pointed out, is likely to result.
I will finish this section on the naming of hybrids with one or two additional points on the correct method of writing their names. Here are the full names of three cultivated hybrids:—
Rubus (rusticanus inermis X thyrsiger) 'Merton Thornless.' Camellia X Williamsii 'Donation.' Rose (Hybrid Tea) 'Richmond.'
The following points should be noted:—
(a) If a formula or a vernacular designation is used as a second part name, it should be placed in brackets between the generic name and the cultivar-name.
(b) If a Latin name is used as a second part name, and the hybrid is between plants belonging to the same genus, a multiplication sign should be placed between it and the generic name.
(c) The third part cultivar-name follows directly on the second part name and is placed in single quotes, as for cultivar-names of non-hybrids.
In many contexts it would not be necessary to write the second part name at all, but if it is omitted, the cultivar-name, strictly speaking, should be preceded by a multiplication sign, thus: Camellia X 'Donation,' but it would be no great crime to omit it, except perhaps in technical publications.
3. What Is the "Correct" Name for a Cultivar?
It is a painfully familiar fact that many cultivars are known by more than one name, and that many cultivar-names have been applied to more than one cultivar—although the position is not so bad as it is in the case of botanical names! This multiplication of names is the inevitable result of many people naming many plants over a period of many years. It is a situation which we must accept and do our best to mitigate. The Code has a number of necessarily rather complicated provisions aiming at selecting the correct name for any cultivar. These provisions are important mainly to the comparatively few horticulturists and botanists who take on the unenviable job of sorting out the nomenclature of cultivated plants, though the results of their labours affect us all. The rules are set out fully in the Code, and here I will attempt only to pick out one or two of the more important.