BOTANY AS APPLIED TO VETERINARY SCIENCE. 259 
1. The seed has two, or rarely more, cotyledons (hence 
the term dicotyledon) or seed-lobes, which are placed oppo¬ 
site each other, representing the undeveloped leaves. This 
may be observed in the germination of the garden bean 
{Faba vulgaris ). 
2. The stem will be found to consist of three principal 
structures—pith, wood, and bark, connected by a number 
of radiating lines called medullary rays. The stem increases 
in size by annual additions of new matter, taking place from 
within outwards (hence the term Exogen), between the 
pith and the bark. If we examine a transverse section of 
the stems of some of our larger trees, such as the elm ( Ulmus 
campestris) , or oak ( Quercus pedunculata) , we shall observe a 
number of concentric ring's with lines radiating from the 
centre. These rings are the annual depositions of new 
material, and as only one of these takes place yearly, the 
age of the tree may be ascertained by their number. The 
radiating lines are the medullary rays. 
3. Leaves in exogenous plants will be found to have their 
veins branching in various directions, anastamosing and 
forming a kind of network, generally distinctly articulated 
to the stem, and of many shapes. This may be well seen in 
the leaves of the currant ( Ribes rubrum), the cherry ( Cerasus 
communis ), and others. 
4. Flowers .— Each part of the flower generally consists of a 
division into four or five parts, or some multiple of that 
number. This may be observed in the common wall-flower 
(Cheiranthus chari ). 
These, then, are the four principal characters by which 
Exogens are distinguished. There are other minor distinc¬ 
tions, but these it will not be necessary for me to enter into 
n this brief outline. 
2. ENDOGENS OR MONOCOTYLEDONS. 
The chief representatives of this class of plants in this 
country are the grasses and sedges, few of which acquire 
the magnitude of trees, although in warmer climates they 
attain a great size, such for instance, as the palms, &c. En- 
dogens or Monocotyledons may be known by the following 
characters: 
1. The seed has only one cotyledon, or seed-lobe; hence 
the term Monocotyledon. An example of this is seen in the 
wild tulip (Tulipa sylvestris). 
