Nevertheless the knowledge of individual forms in these organisms had been considerably extended before 1850. Collectors and amateurs, intent only on determining what is immediately presented to the eye and making little enquiry into origin and affinities, were indefatigable in adding to their collections, and made catalogues and proposed various systems founded on external marks taken at pleasure. The names of species were counted by thousands, their characters filled thick volumes and the figures large folios; the abundance of forms in the Thallophytes proved to be so great that many botanists devoted their whole attention to them, many collected and described only the Algae, others only the Fungi and Lichens. It is true that a deeper insight into the connection of these forms of life with one another and with other plants was not to be obtained in this way; still an empirical basis was formed for a knowledge of the Cryptogams, such as had been established for the Phanerogams by the herbals of the 17th century. All forms open to observation were named and arranged in one way or another; and there was no difficulty in understanding what form was meant, when names, or tables and figures, were cited from the various books. Of such works, those of Agardh[56], Harvey, and Kützing on the Algae, those of Nees von Esenbeck[57], Elias Fries, Léveillé, and Berkeley on the Fungi, and especially Corda’s elaborate work on the latter plants are the most valuable. The views entertained on the subject of the development and propagation of the lower Cryptogams down to the year 1850 were very uncertain and fluctuating. In some Algae, Fungi, and Lichens certain organs of multiplication and propagation were known, in others they were quite unknown; some forms appeared in places and under circumstances which seemed to necessitate the assumption of spontaneous generation; in 1827 Meyen declared that the small Algae, known as ‘Priestley’s matter,’ which are formed in stagnant water and even in closed vessels, are produced by free generation, and Kützing endeavoured to show this by experiment in 1833; some Fungi were regarded as diseased growths from other organisms, many were supposed to spring up spontaneously, though they might be capable at the same time of propagating themselves by spores; this view was shared by even the best botanists with regard to the most simple Fungi up to 1850. But the systematic investigation of the Algae and Fungi was as little hindered by the notion of spontaneous generation after 1850 as that of Phanerogams had been in the 17th century by the same notion; it was however at first affected by the view put forth by Hornschuch in 1821 and by Kützing in 1833, that the simplest of all Alga-cells (Protococcus and Palmella), once produced spontaneously, could develop according to circumstances into a variety of Algae, and even of Lichens and Mosses; as some observers even now consider Penicillium and Micrococcus to be the starting-points