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GARDENERS' CHRONICLE 



Length of Life in Plants 



WILLARD N. CLUTE 



THE customary classification of plants as annuals, 

 biennials and perennials is more a matter of con- 

 venience than an expression of the exact situation 

 with regard to the length of life in plants. The majority 

 of annuals, for instance, do not live for even a full year. 

 A single growing season often measures their span of 

 life and many others, such as the little whitlow grass 

 (Draba), are able to condense their whole existence 

 into a period of five or six weeks. Un the other hand, 

 some of our annual weeds spring up in Autumn and pass- 

 ing the Winter as seedlings mature their fruits the follow- 

 ing Summer, thus living in two growing seasons but 

 seldom existing for more than a year. These latter plants 

 are often called "winter annuals" to distinguish them 

 from the more common kinds, which begin their growth 

 in Spring. The wild lettuce is naturally a Winter annual 

 and wheat becomes so when sown in the Fall. 



The biennial is another mental conception rather than 

 a plant entity. As commonly understood it is a plant 

 that requires two years for the completion of its life 

 cycle, but after a consideration of its behavior we see 

 that it is really two growing seasons, rather than two 

 years, that are involved. This point is important because 

 in warm regions, where the growing season is longer, 

 there are practically no biennials. There they are able to 

 complete their work in a single year. Alorever, in any 

 considerable area devoted to the so-called liiennials, it 

 is not uncommon to find specimens that are able to fruit 

 the first season. The essential thing is the way in which 

 food is used. One group, like the goldenrods and asters, 

 make their food as they go along ; the other accumulates a 

 store of food before blooming. The biennials belong 

 to this latter class. The garden radish clearly illustrates 

 the process, first storing food in its large root and then 

 producing flowers and fruits. It differs from the bien- 

 nials, however, in compressing all its activities within a 

 single growing season. The storage of food by the bien- 

 nials is what makes them such important food plants. We 

 simply appropriate the food-stores before the plant has 

 had time to use them. 



While the biennial garden plants are the most familiar 

 instances of food storage before blooming, they are by 

 no means the most remarkable. Many other plants 

 require not two years but many years, before they are 

 able to put up a flower-spike. Of this class the centun- 

 plant is a fine example. It is commonly supposed that 

 such plants require a hundred years of growth to come 

 into bloom, but however this may be in conservatories, 

 in their native haunts from ten to twenty years is usually 

 enough. The talipot palms of the Old World come much 

 nearer being century plants for they often live for fifty 

 years or more before blooming. Like the annuals, how- 

 ever, when once thev blossom, they rapidly decline and 

 die. The common yucca is another example of this group 

 of plants, but it is to be noted that the yucca and several 

 others do not die after flowering. The part that bears 

 the flowers dies, but from the base of the old stem new 

 sprouts are put forth which carry on the work. The 

 yucca then, is a sort of perennial with many of the char- 

 acteristics of an annual. 



The feature that distinguished the true perennials from 

 the classes already mentioned is not the fact that they 

 live for a term of years but that they bear flowers and 

 fruits more than once. Considered from this angle, we see 

 that a more definite dividing line is possible. It is easy to 



make two groups of all flowering plants depending upon 

 whether they bloom once or more than once. Those 

 which bloom but once are known as monocarpic plants 

 and the others are called polycarpic plants. But just as 

 the line between annuals and biennials breaks down in 

 warm regions, the line between monocarpic and polycar- 

 pic plants breaks down in a cold one, at least in the case 

 of polycarpic plants transferred from one region to the 

 other. Many polycarpic plants of the tropics become 

 monocarpic plants when brought into northern gardens. 

 The four o'clock is a good example. This is really a 

 perennial but it so rarely becomes so with us that most 

 people suppose it to be an annual. If preserved from the 

 cold, however, it will quickly resume growth in Spring 

 and come into bloom much earlier than plants grown 

 from seeds. One seven-year-old plant in the writer's 

 possession produced more than five thousand blossoms 

 during the past Summer. Another way in which the 

 line appears to be broken down by the polycarpic plants 

 is by their blooming the first season from seeds. Poly- 

 carpic plants are noticeably slower in development than 

 the annuals and biennials. Frequently it is possible to 

 decide whether an unknown plant is a perennial or not 

 by the comparative rapidity of its growth. Most peren- 

 nials do not bloom the first year from seed and many 

 vegetate for fifteen years or more before putting out the 

 first crop of blossoms. There are a number of polycarpic 

 plants, however, in which the ability to produce more 

 than one set of blossoms is not very firmly fixed. The 

 hollyhock, the snapdragon, and many columbines, pent- 

 stemons and pinks are good illustrations. After the 

 first full season of bloom they tend to disappear though 

 with care they may be induced to bloom for a series of 

 years. On the other hand, there are others that fre- 

 quentlv bloom twice in the same season, especially if, as 

 in the past Summer, conditions are such as to nearly 

 check growth in Midsummer. A wet Autumn makes 

 a second Spring in which great numbers of plants bloom 

 again. I have found all of our Spring flowers blooming 

 thus in dilferent years. 



From the fact that annuals and biennials are most abun- 

 dant in cold or dry regions it seems pretty certain that 

 such forms are a response to peculiar climatic conditions 

 in their environment. They are able to persist in regions 

 where a part of each year is hostile to growth by springing 

 up and ripening their seeds before the inhospitable season 

 overtakes them. Moreover, in such situations they are 

 practically relieved from the competition of the stronger 

 perennials which usually overwhelm them in more in- 

 viting situations. In the tropics the vegetation is prevail- 

 ingly woody. It has been estimated that in some sec- 

 tions only 12 per cent, of the flora is herbaceous. An- 

 nuals of any kind are naturally extremely scarce. When 

 annuals do occur in favorable regions, their short term 

 of life is also of advantage in giving them more mobility. 

 Most gardeners can call to mind perennial plants that 

 appear to avoid spots in which they have once grown, 

 each year spreading away from the center until they form 

 what in simpler plants are known as "fairy rings." An- 

 nual plants find it easy to desert such a place. The trees of • 

 all others appear to be in the worst case because they can- 

 not get away, but it must be remembered that their roots 

 spread away from the center like the others and thus 

 while the main body remains, the roots ever feed in new 

 regions. (Continued on page 773) 



