[160] Paper bags also may be made use of. They are slipped over the flowering branches, and bound together around the twigs, thus enclosing the flowers. It is necessary to use prepared papers, in order that they may resist rain and wind. The best sort, and the one that I use almost exclusively in my fertilization-experiments, is made of parchment-paper. This is a wood-pulp preparation, freed artificially from the so-called wood-substance or lignin. Having covered the flowers with care, and having gathered the seeds free from intermixtures and if possible separately for each single individual, it only remains to sow them in quantities that will yield the greatest possible number of individuals. Reversions are supposed to be rare and small groups of seedlings of course would not suffice to bring them to light. Only sowings of many hundreds or thousands of individuals are decisive. Such sowings can be made in one year, or can be extended over a series of years and of generations. Hildebrand and Hoffman have preferred the last method, and so did Hofmeister and many others. Hildebrand sowed the white hyacinth, and the white varieties of the larkspur, the stock and the sweet pea. Hoffman cultivated the white flax and many other varieties and Hofmeister extended his sowings [161] over thirty years with the white variety of the yellow foxglove (_Digitalis parviflora_). White-flowered varieties of perennial garden plants were used in my own experiments. I bought the plants, flowered them under isolation in the way described above, gathered the seeds from each individual separately and sowed them in isolated groups, keeping many hundreds and in some cases above a thousand plants up to the time of flowering. Among them I found only one inconstant variety, the white form of the yellow columbine, _Aquilegia chrysantha_. It evidently belonged to the group of sporting varieties already referred to. All others came absolutely true to type without any exception. The species experimented with, were _Campanula persicifolia_, _Hyssopus officinalis_, _Lobelia syphilitica_, _Lychnis chalcedonica_, _Polemonium dissectum_, _Salvia sylvestris_ and some others. Tested in the same way I found the white varieties of the following annual plants also quite true: _Chrysanthemum coronarium_, _Godetia amoena_, _Linum usitatissimum_, _Phlox drummondi_, and _Silene Armeria_. To these may be added the white hemlock stork's-bill (_Erodium cicutarium album_) which grows very abundantly in some parts of my fatherland, and is easily recognizable by its pure green leaves and stems, even when not flowering. I cultivated it, in large numbers [162] during five succeeding generations, but was never able to find even the slightest indication of a reversion to the red prototype. The scarlet pimpernel or _Anagallis arvensis_ has a blue variety which is absolutely constant. Even in Britton and Brown's "Flora," which rarely enumerates varieties,