218 
On the Simple Structure 
t Monthly Microscopical 
Journal, April 1, 1869. 
produced basifugally. But the Sycamore cannot be compared witli 
that of the Horse-chestnut, because the Horse-chestnut is in reahty 
a ternate leaf (hke the Oriental Plane), the three parts being of 
the first order, while the rest are produced by bifurcation of the side 
parts of the first order. 
The leaves of Dicotyledonous plants develop in various ways. 
We may refer them to six types : * — 
Type 1. Basifugal. — The apex of the leaf the youngest, the 
base the oldest. When parts of the second order are present, they 
are also basifugal. 
A very good and easily procured example of this type is to be 
found in the Garden-Pea, as well as all Leguminosdd with true 
pinnate leaves, and several Umhelliferse. 
Type 2. Basipetal. — The apex of the leaf the oldest, the base 
the youngest. In this type the parts of the second order may 
either develop basipetally, as in Bosa, Fotentilla, Poterium, &c. ; 
or basifugally, as in Acer Pseudo-Flatanus, and other species of 
Acer. 
Type 3. Divergent. — The leaves of Achillea, Pyrethrum, and 
other Composite, have the parts of the first order developing 
towards both ends from the middle of the leaf ; and, when secondary 
parts are present, they develop also divergently in relation to the 
parts of the first order, but basifugally if a single division only is 
taken into account. 
Type 4. Terncde. — Here we have two opposite parts developed 
from one of a higher order. Trifolium, Cytisus, and Fray aria 
represent the type. If parts of the second order are present, they 
may be ternate, as Aquileyia, Thalictrum, &c. The parts of the 
second order may be ternate, but in the parts of higher orders only 
the middle part, or one of the side-parts ternate, as Aralia spinosa, 
Thalictrum flavum, &c. ; or, lastly, parts of the second order may 
be produced as bifurcations of the side-parts of the first order. This 
is well seen in Platanus, JEsculus Hippocastanum, Banunculus, 
Aconitum, &c. 
In these four types the parts of the leaf are developed by the 
edges of the epiphyll only ; in the next two types the parts of the 
leaf are developed from the inner side, as weU as the edges of the 
epiphyll. 
Type 5. Cyclical. — To this type peltate leaves belong, and 
they may develop their parts in various ways, but most frequently 
basipetally. As examples, we may take the Tropseolum, Castor oil, 
Geranium, Lupin, &c. 
Type 6. Parallel. — In this type we have the parts of the leaf 
developed in vertical rows on both sides of the middle line, and 
parallel to the marginal rows. To this type belong many of the 
* See ' Trans. Bot. Soc, Edin.,' vol. viii., pp. 381 and 400. 
