In general, starch is the final product of photosynthesis in most green plants; but there are many exceptions to this. The polysaccharides, which are generally insoluble, must be broken down into the simpler soluble sugars before they can be translocated to other organs of the plant for immediate, or future, use. When they reach the storage organs, they may be recondensed into insoluble polysaccharides, or stored as soluble sugars. Examples of the latter type of storage are, sucrose in beet roots, glucose in onion bulbs, etc. Sometimes, this habit of storage seems to be a species characteristic; as potatoes store starch, while beets, growing in the same soil and under exactly the same environment, store sugar. But in other cases, the nature of the carbohydrate stored undoubtedly is correlated with the external temperatures at the time of storage. It has been shown that cold, which tends to physiological dryness, very frequently favors the storage of sugars instead of starches. Thus, in temperate zones, among aquatic, or moisture-loving plants, those species which hibernate during the winter at the bottom of lakes or ponds and are killed by temperatures below freezing, store starch and no sugar; while in the same ponds, the species whose storage organs pass the winter above the level of the water and can withstand temperatures as low as -7° C. contain sugar during the winter months, even if they contain starch during warmer periods. Similarly, sugars often appear in the leaves and stems of conifers during the winter months, only to disappear, or be replaced by starch, when spring approaches. This same phenomenon is noticeable in arctic plants, which generally contain but small proportions of starch and relatively large amounts of sugars. Similarly, the phenomenon of the turning sweet of potatoes when exposed to low temperatures has often been noted. The change of the starch in potato tubers to sugar is most rapid at the temperature of 0° C., and ceases at 7°, or above. Also, if potatoes in which the maximum amount of sugar is present (not over one-sixth of the total starch can be converted into sugar) are exposed to a higher temperature the sugar soon disappears. In general, however, it may be said that each particular species of plant has its own particular preference for a specific carbohydrate as its reserve food material, and elaborates the proper enzymes to make it possible to utilize this particular carbohydrate for its metabolic needs.