SOME EEMARKS ON THE TERMS ASNUAL AND 

 BIENNIAL. 



By T. R. Akcher Briggs, F.L.S. 



There are difficulties in assigning plants severally to two of 

 the three divisions employed to mark the period of theii* duration : 

 in other words, it often seems open to doubt whether a certain 

 species should be accounted Annual or Bimyiial. More minute 

 division seems required to define quite accurately the duration of 

 many plants than that rendered possible by the use of the three 

 terms, Annual, Biennial, and Perennial. At present there are 

 species put together under two of them, viz., annual and biennial, 

 that differ considerably among themselves as to length of life and 

 period of growth. 



Annual, the term employed to express the shortest period of 

 plant-existence, now includes under it species whose duration is 

 considerably less than that of twelve calendar months. Here we 

 find some Atriplices, Chenojjodia, &c., together with many weeds of 

 cultivation, which spring up in April or May and die in October or 

 November. Of still shorter duration are often several species ; 

 the common little grass, Poa annua, for instance, whose whole 

 period of existence is sometimes limited to four or five months. 

 But together with the plants just named, annual now also includes 

 not only the species to which it best and most strictly apphes — viz., 

 plants that vegetate from seed in early spring and last until the 

 succeeding winter — but also many kinds of Geranium, Trifolium, &c., 

 which spring up in late summer or autumn from seed then 

 recently shed, live on through the winter, flower the next spring 

 or summer, bear seed, and then die. The life of these last 

 consequently extends over a portion of two years, though it is not 

 ordinarily prolonged beyond twelve months. This being the case, 

 it follows that they may strictly be held to be annuals only, yet by 

 so considering them we abolish all distinction between them and 

 plants whose whole life does not extend beyond half this time. 

 Sometimes a plant living for so short a period as six or seven 

 months only will nevertheless have this time made up of parts of 

 two different years. Draha venia, for instance, may occasionally 

 be found sufficiently advanced to produce some flowers before the 

 end of December, and may be seen shedding seed by the end of 

 March. The most truly biennial plants are those of the nature of 

 Erysimum Alliaria and Digitalis j^urpurea, species that shed seed in 

 summer or autumn which does not vegetate until the next spring. 

 The young plants then produced continue to increase in size until 

 the succeeding winter, live through it without growing much, but 

 in the next spring start into vigorous growth, and during this 

 second year of then- existence flower, produce seed, and then die. 



