PLANT ORGANS AND ORGANISMS 213 



Between each nbro-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 mtta 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 denned in the region of 

 the rap he. 



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- 



