LIFE HISTORY AND RACE HISTORY 
15 
spines as in the Canon Gooseberry (Ribes californicum). In the forma¬ 
tion of the scales of the winter bud leaves also play an interesting part. 
Sometimes the scale of the winter bud is the equivalent of a leaf blade, as 
in the case of the Madrono (Arbutus menziesii) ; sometimes it is the 
equivalent of a dilated petiole, as in the California Buckeye (Aesculus 
californica) ; or yet again the scales are stipular, since they occur in pairs, 
as in the case of the California Hazel (Corylus rostrata var. californica). 
The morphology of an organ can only be determined by studying it 
carefully, by keeping in mind the following considerations: position, 
structure, shape, size and color. The first, position, is of very great im¬ 
portance ; structure is also of great importance, shape is of some im¬ 
portance, size of slight importance and color almost none at all. The 
untrained mind, it is interesting to note, takes the importance of these 
characters in reverse order. 
Root, stem, and leaf and their modifications constitute the vegetative 
organs of the plant and are always to be sharply differentiated from the 
sexual reproductive organs. The sexual reproductive organ is the flower. 
Typically it consists of four circles of organs borne upon a receptacle. 
1. A calyx consisting of a circle of units called sepals or calyx-lobes. 
2. A corolla consisting of a circle of units called petals or corolla 
lobes. 
3. An androecium consisting of a circle of units called stamens. 
4. A gynoecium consisting of a circle of units called carpels or simple 
pistils. 
The parts of a typical flower occur in regular circles or spirals with the 
parts or units alternating regularly, but in the course of evolution the 
units have been subject to multiplication or diminution or suppression. 
In general, in a given family, we regard the primitive type of flower as 
having both stamens and pistils. The loss or suppression of stamens 
and pistils results in unisexual flowers which we regard as derived. The 
Meadow Rue (Thalictrum) is unisexual in the family Ranunculaceae 
where perfect flowers are general and where the simplest forms in the 
family have perfect flowers. A calyx consisting of distinct sepals (chori- 
sepalous) is regarded as more primitive than one with united sepals (syn- 
sepalous), just as a corolla with distinct petals (choripetalous) is re¬ 
garded as more primitive than a flower with united petals (sympetalous). 
The carpel has often been likened to a leaf with its two margins united 
to form a cavity, the midrib corresponding to the dorsal side, the ovules 
borne along the united or ventral side on specialized tissue which is called 
a placenta. Such a pistil is called a simple pistil and is considered primi¬ 
tive. If a pistil is compound, that is composed of two or more units or 
simple carpels, it is considered an advance. Two or more carpels may 
be united in such a way as to make a single pistil but with 2 or more cells 
and the placentae diverging from the axis, or the carpels may be united 
by their margins so as to make a single pistil with only one cell and the 
placentae borne on the side walls. When two or more carpels are joined 
to form a single compound pistil the evidence of it is usually readily de¬ 
termined by the student observing the number of stigmas and styles. 
Sometimes, however, the styles and stigmas are so completely blended 
