THE FAMILY CHAIN 355 
dehisce by longitudinal slits. The expression T ~ means that the 
torus is convex and implies that the perianth and andrceecium are 
hypogynous. When as in Peonia they are perigynous this is indi- 
cated by T ~ which represents the torus as concave. 
The form of the ovules is shown by a mark placed over their 
numerical sign, a circumflex accent-mark meaning that the ovule 
is anatropous. Their ventral position is understood in simple 
pistils, while in compound pistils like that of Nigella, the single 
parenthesis after the number of carpels implies that the ovules are 
on an axile placenta. 
When the pericarp becomes fleshy as in Actza this is indicated 
by an exclamation mark after the C. When the pericarp is dry, 
as in Caltha, there is instead an inverted exclamation mark. Inde- 
hiscence is indicated by the sign <. When the pericarp dehisces 
along a ventral suture as in Caltha, etc., the sign < is employed. In 
all the formulas the expression G-N implies that the embryo is 
uncoiled within albumen. 
The scheme of plant formulas which is here proposed and which 
will be further elaborated in the following pages, is an extension 
and modification of the floral formulas used by many botanists. 
As a sort of botanical shorthand of wide application it is believed 
that the student will find it not only labor-saving but helpful in 
grasping plant relationships. After a little use, what seemed strange 
will have become familiar and a glance will discover important 
characters that might easily escape notice in comparing equally 
full verbal descriptions. 
105. The family chain. Having learned the signification of 
these symbols we are now in position to use the formulas as a ready 
means of comparing the main structural features of our representa- 
tive genera to see how they are linked together. Take, for instance, 
Caltha and Pxonia. If we conceive of a marsh-marigold having a 
concave torus, a perianth differentiated into calyx and corolla, and 
pinnately compound leaves, such a plant would be classed as a 
peony. By these same features, however, it might be distinguished 
from all the other genera. Therefore, although closely linked with 
Caltha, Peonia is placed on a line apart in the tabular view. 
Helleborus differs from Caltha chiefly in having the carpels some- 
times coalesced and in possessing staminodes. In these respects 
it is a link connecting Caltha with Nigella which has the carpels 
always coalescent, and differs from Helleborus only in having 
pinnate instead of palmate leaves, some of which may be so near the 
flower as to constitute an involucre, and in consisting of annual 
rather than perennial herbs. 
Aquilegia, with its carpels distinct, is more like Caltha, but 
differs from both Caltha and Nigella in having the carpels always 
five, staminodes in two inner sets of five and one outer set of the 
same number, and in having the leaves ternately decompound. 
