PLANT ORGANS AND ORGANISMS 
213 
Between each fibro-vascular bundle and the tip of each rib will be 
found a zone of collenchyma cells. In the mesocarp between each 
two ribs on the dorsal side occurs a single vitta or oil tube which is 
lined with a layer of brownish polygonal cells. These vittae contain 
the official oil of fennel. Two vittae generally occur in the meso¬ 
carp of the commissural side although four are reported to have 
been found in this region of some fennel fruits. 
3. Endocarp , a narrow layer of cells, transversely elongated, except 
over the regions of bundles where they may be seen elongated in 
several directions. 
4. Spermoderm or Seed Coat , consisting of a layer of somewhat 
broadened epidermal cells attached to the endocarp and several 
layers of collapsed cells which are only well defined in the region of 
the raphe. 
5. Endosperm , a central mass of more or less polygonal cells con¬ 
taining aleurone grains and oil globules. Each aleurone grain con¬ 
tains a rosette aggregate of calcium oxalate and one or two globoids. 
6. Embryo, embedded in the endosperm of the upper region of the 
seed. 
THE SEED 
A seed is a matured megasorus (ovule) borne by the sporophyte of 
a spermatophytic plant, enclosing a megaspore (embryo sac) within 
which a fertilized egg of the succeeding gametophyte generation has 
segmented to form a new sporophyte plant. The purpose of the 
seed is to insure the continuation and distribution of the species. 
Like the ovule, it consists of a nucellus or kernel enclosed by integu¬ 
ments, and the descriptive terms used are the same. The seed 
coats, corresponding to those of the ovule, are one or two in number. 
If but one seed coat is present it is termed the spermoderm. If two 
are present, the outer one is called the testa , and the inner one the 
tegmen. The testa, or outer seed shell, differs greatly in form and 
texture. If thick and hard, it is crustaceous; if smooth and glossy, 
it is polished; if roughened, it may be pitted, furrowed, hairy, reticu¬ 
late, etc. 
The testa may often present outgrowths or seed appendages whose 
functions are to make the seeds buoyant, whereby they may be dis- 
