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REPRODUCTION OF PLANTS. 
There is not a more interesting phenomenon in the history of the vegetable 
kingdom, than that of the constitutional power of plants to reproduce themselves. 
The production of seed to perpetuate the species is the grand purpose of their being. 
The life of many plants is limited to this principal effort, and when completed they 
instantly die. This circumstance has gained for certain descriptions of plants the 
titles of annuals, biennials, and perennials. Annuals spring up, perfect their seeds, 
and die in the course of one season; biennials require parts of two summers to 
arrive at perfection ; the life of perennials is not limited to the act of ripening seed, 
but to the durability and spreading properties of their roots. There is another 
description of plants which do not come in under any of those titles, though their 
production of flowers or seed terminates their life. These are such as require an 
uncertain number of years to bring them to perfection, and which are more or less, 
according to the circumstances of soil and temperature in which they happen to be 
placed. The Agave Americana, commonly called the American Aloe, arrives at its 
utmost magnitude and perfects its seeds in the short space of four or five years 
in its native climate ; whereas when kept as a greenhouse plant in this country, 
forty, fifty, or more summers must elapse before it puts forth its flower-stem, which 
is the final effort of the plant. 
Vegetables resemble animals in being sexual; that is, they have male and 
female organs on the same or on different plants : and without the mutual influ- 
ences of these, no perfect seeds can be matured. The greater number of plants 
have bisexual flowers ; in this case, there is but little risk of failure of perfect seed, 
because the essential organs are so near together. Some are bisexual plants, that 
is, having unisexual flowers distinct from each other, but on the same root. 
Others are unisexual plants, that is, the male flowers are on one plant, and the 
females on another. It may easily be conceived that unless, in this last case, both 
plants stand near together, no perfect seed can be expected. There is yet another 
disposition of unisexual and bisexual flowers, called polygamous, in which male 
flowers are on one plant, females on another, and male and female on a third. 
This remarkable disposition is exemplified in the fig. 
Thus there are bisexual flowers : — examples, the tulip and the rose ; bisexual 
plants, as the oak and hazel ; unisexual plants, as the poplar and willow ; and poly- 
gamous or anomalous plants, as is exhibited in the genus fig. 
These are the provisions of nature intended for ensuring the maturation of 
seed, and by which the dissemination of the different species of plants is maintained. 
Even those tribes of vegetables which have no visible flowers, viz. all the 
cryptogamous orders of ferns, mosses, lichens, hepaticae and fungi, have nevertheless 
the hidden power of discharging parts of themselves called sporules, which are 
endowed with all the properties of perfect seeds ; because wherever they fall 
on soil or other substance favourable to their growth, there they fix themselves 
and prosper. 
