Although, at first, Darwin was able to enumerate less than a dozen naturalists who were prepared to accept his views, while influential leaders of thought in science--like Richard Owen in this country and Louis Agassiz in America--were bitterly opposed to them, the theory gradually obtained supporters especially among the younger cultivators of botany, zoology and geology. It is evident that Darwin for some time regarded his 'abstract,' as he called the _Origin of Species_, as only a temporary expedient--one to be superseded by the publication of the much more extended work, designed and commenced long before. Although the _Origin_ was only published late in November 1859, and he was called upon immediately to prepare a second edition, we find that on January 1st, 1860, Darwin began to arrange his materials for dealing with the first great division of his subject, 'the variation of animals and plants under domestication.' So numerous and important were his notes and records of experiments, however, that he soon found that to expand the whole of the 'abstract,' on the same scale, would be an impossible task for any one man, however able and diligent. Unwilling that the results of some of his special researches should be lost, he wisely determined to issue them as separate books. The first of these to appear was that on the _Fertilisation of Orchids_, a beautiful illustration of the relation of insects to flowers in producing crossing. He had been more than twenty years working and experimenting on this subject, his interest in it having been quickened by having read an almost forgotten book of the botanist Sprengel. Almost at the same time, and in following years, he wrote papers for the Linnean Society on dimorphic and trimorphic forms of flowers, and their bearing on the question of cross-fertilisation. These papers were the foundation of his well-known work, _The Different Forms of Flowers on Plants of the same Species_. In the same way, a paper read in 1864 to the Linnean Society was subsequently expanded into _The Movements and Habits of Climbing Plants_. Owing to delays caused by the preparation and publication of these books and frequent interruptions from sickness, the work on variation did not appear till 1868. It was a very extensive piece of work in two volumes, and, at its end, Darwin tentatively propounded a hypothesis to account for the facts of Heredity and Variation to which he gave the name of 'pangenesis.'