Other inhabitants of the stony wastes of South Africa are the ‘stone plants’ or ‘living pebbles’ — mem-bers of the genera Lithops, Conophytum and Pleio-spilos. All are ‘window plants’. Their leaves are extremely succulent, round or cylindrical, with blunt tips furnished with windows in the form of irregular marbling or small translucent dots. In general they are not coloured green but tinted red, brown, bronze or grey as protection against the sun. The cells containing chlorophyll and carrying on the process of photosynthesis are located inside the body behind a layer of cell tissue that disperses the light.
Because these are very small, often even miniature plants, a great many can be grown in a small space and thus are ideal for the collector. However, they are very sensitive, requiring not only full sun and cool but well-lit conditions in winter but, first and foremost, tolerating no mistake in watering.
Most of the 70 species of the genus Lithops have their growth period in early spring, from February to April. The groove in the body opens and from this grows a small new plant which takes its food and water from the old one. At this point most beginners start watering the plant, thereby destroying it com-pletely. In fact, it should be watered only lightly, just so the compost is moistened and dries out again right away, from late May until early September, or at most October — in other words during the period of relative rest. After that, water should again be withheld for about 7 months. Only thus will the grower be rewarded with a thriving plant that will produce attractive large. These appear between June and October, depending on the species.
The compost should be very free-draining, sandy and stony, with an addition of leaf mould.