250 GLOSSARY 



dioxi(l(\ Tt is cavricd on l>y the cliromatophores and chloroplasts 

 acted on l)y the energy of snnlight. 



Physiology. The science of tlie action and fnnctions of organisms. 



Pinnate (a feather). Having leaflets arranged along two sides of a main 

 leaf axis. 



Pistil (a pestle). The simple or componnd structure (composed of one 

 or more carpels) which in angiosperms contains the ovules. 



Placenta. The ovule-bearing portion of the interior of the ovary. 



Plageotropic (oblique turning). Assuming an oblique direction under 

 the influence of gravity, as most secondary roots. 



Plasma membrane. The limiting membrane of a protoplast. 



Plasmolysis (that w^hich is formed, loosing). A separation by osmotic 

 action of the protoplast from the cell wall. 



Plastid (that formed). A protoplasmic body usually with a special func- 

 tion. The term is used collectively for chloroplasts, chromoplasts, 

 and leucoplasts. 



Plerome (that which fills). That part of the meristem near a growing 

 point wdiich is surrounded by the periblem and develops into the 

 central cylinder. 



Plumule (a little feather). The primary leaf bud of an embryo seed 

 plant. 



Pod. A dry, many-seeded, dehiscent fruit. 



Pollen (fine flour). Minute grains developed in the pollen mother cells 

 of the anther and essential for the fertilization of the ovule. The 

 locules of the anther are morphologically microsporangia and the 

 pollen grains are microspores. 



Pollen tube. The structure which is developed from the inner coat of the 

 pollen grain and serves to carry the sperm nuclei into the embryo 

 sac of the ovule. 



Pollination. The transference of the pollen to the stigma or to the 

 naked ovule of the gymnosperms. 



Prosenchyma. Tissue composed of elongated cells. 



Proteid. Any one of a group of nitrogenous compounds of which albu- 

 men is an example. 



Prothallium (before a young shoot). The gametophyte developed from 

 the spore of a pteridophyte. 



Protonema, plu. protonemata (first thread). A filamentous growth devel- 

 oped from the spore of a moss, from which the leafy moss plants 

 arise. ' 



Protoplasm (first formed). The living part of the material of the plant 

 or animal body contained in the cells. 



Protoplast. A unit of protoplasm, or cell, with or without a cell 

 wall. 



Pteridophytes (fern plants). The great group composed of the ferns, 

 horsetails, and club mosses. 



Pyrenoid (resembling a kernel). Minute bodies imbedded in the cliro- 

 matophores, which act as centers of starch formation. 



