OBSERVATIONS FOR YOUNG BOTANISTS 153 
the period of vegetative growth is declining, and tliat of 
flowering coming on, the leaves gradually cease to be formed, 
and are then reduced to bracts by being arrested in growth. 
In addition to this, bracts may now partake somewhat of the 
nature of corollas and become white or brightly coloured, so 
that they can assist in rendering the flower attractive to insects, 
which come for honey or pollen, and so “ pollinate” the flower. 
As an e.xample may be mentioned the well known Poinsettia, 
used as a decorative plant in winter, with its brilliantly scarlet 
leaf-like bracts ; and some salvias have not only scarlet corollas, 
but scarlet calyx and bracts as well. 
In some instances the bracts may surround a dense cluster 
of flowers, as in the CompositiF. They are then collectively called 
an “involucre,” as in the daisy and dandelion. In these two 
flowers the involucres are green ; but in some they are white, 
yellow, red, &c., and can easily be taken for a corolla, as in 
the so-called “ everlastings.” 
Again in some cases they imitate a flower more exactly, as 
in certain species of cornel (Coni/is), the inflorescence of which 
consists of a dense mass of very insignificant looking flowers, 
with four large white bracts, very suggestive of a white-flowered 
clematis. 
Another shrub-like plant, called Darwinia tidipifeya, belonging 
to the myrtle family, bears inflorescences which, to the un- 
initiated, look like coloured tulips hanging down all over the 
bush. These are composed of brightly coloured bracts, within 
which are some dozen of very small flowers. 
Another result of a change of nature from leaves to bracts, 
especially on poor soils and in a dry atmosphere, is to reduce the 
bracts almost entirely to spines. Thus the star-thistle {Ccntaurea 
Calcitrapa) has the bracts of the involucre terminating in long 
sharp points. It has got its specific name from the resemblance 
to a “ caltrop,” an iron ball with four spikes used for impeding 
cavalry. This plant is the “thistle” of the desert mentioned 
in Scripture. It is rare in England. 
A curious form of bract is seen in the so-called “ spathe ” 
of our common lords-and-ladies [Arum maculatum). The culti- 
vated “ arum-lily ” has a white one, though in other species it 
is yellow, scarlet, &c. 
Inflorescences. — -The simplest kind of inflorescence is 
where the flowering shoot is terminated by a single flower, as 
in the tulip and buttercup. If the same stem bear any more, 
the flowers must arise from points helow the first. All such 
inflorescences are said to be “definite;” but if the shoot 
continue to elongate and the flowers arise one after another in 
an ascending series, as in. a wallflower, fox-glove, and lily-of- 
the-valley, no flower ever terminating the stem, then such is 
called an “ indefinite” inflorescence. 
A stem bearing a terminal flower, or a bunch of flowers as 
in the horse-chesnut, of course, cannot lengthen ; but it often 
