Among the systematists who tested plants in this way, Nageli especially, directed his attention to the hawkweeds or _Hieracium_. On the Swiss Alps they are very small and exhibit all the characters of the pure alpine type. Thousands of single plants were cultivated by him in the botanical garden of Munich, partly from seed and partly from introduced rootstocks. Here they at once assumed the tall stature of lowland forms. The identical individual, which formerly bore small rosettes of basal leaves, with short and unbranched flower-stalks, became richly leaved and often produced quite a profusion of flower-heads on branched stems. If then they were transplanted to arid sand, though remaining in the same garden and also under the same climatic conditions they resumed their alpine characters. This proved nutrition to be the cause of the change and not the climate. The latest and most exact researches on this subject are due to Bonnier, who has gone into all the details of the morphologic as well as of the physiologic side of the problem. [440] His purpose was the study of partial variability under the influence of climate and soil. In every experiment he started from a single individual, divided it into two parts and planted one half on a mountain and the other half on the plain. The garden cultures were made chiefly at Paris and Fontainebleau, the alpine cultures partly in the Alps, partly in the Pyrenees. From time to time the halved plants were compared with each other, and the cultures lasted, as a rule, during the lifetime of the individual, often covering many years. The common European frostweed or _Helianthemum vulgare_ will serve to illustrate his results. A large plant growing in the Pyrenees in an altitude of 2,400 meters was divided. One half was replanted on the same spot, and the other near Cadeac, at the base of the mountain range (740 M.). In order to exclude the effect of a change of soil, a quantity of the earth from the original locality was brought into the garden and the plant put therein. Further control experiments were made at Paris. As soon as the two halved individuals commenced to grow and produced new shoots, the influence of the different climates made itself felt. On the mountain, the underground portions remained strong and dense, the leaves and internodes small and hairy, the flowering stems nearly [441] procumbent, the flowers being large and of a deep yellow. At Cadeac and at Paris the whole plant changed at once, the shoots becoming elongated and loose, with broad and flattened, rather smooth leaves and numerous pale-hued flowers. The anatomical structure exhibited corresponding differences, the intercellular spaces being small in the alpine plant and large in the one grown in the lowlands, the wood-tissues strong in the first and weak in the second case.