282 GLOSSARY AND INDEX. 



pollen-tube, the tute formed in the germination of a pollen-grain, 78. 



pollination, conveyance and application of pollen to the stigma, 83. 



poUinium (pi. polUnia), a pollen-mass, particularly of a milkweed or 

 orchid, 229. 



polycotyledonous, having several or many cotyledons, 14. 



polyembryony, a condition normal in the Coniferse and of exceptional 

 occurrence elsevsrhere, in which more than one embryo, or embryo- 

 rudiment, is formed, 12. 



polygamous, having staminate or pistillate flowers, together with perfect 

 ones, either on the same or on different individuals, 85. 



polygamo-dioecious, having a tendency to the complete dioecious arrange- 

 ment, but producing a greater or less number of perfect flowers, 211. 



prepotency, 86. 



prosenchyma, a tissue consisting of elongated, usually thick-walled cells, 

 which are fusiform or have oblique ends that overlap, such as bast 

 fibers and wood fibers. Prosenchymatous cells are chiefly mechan- 

 ical in function and are mostly destitute of protoplasm. 



protection, 10, 32, 47, 61, 83, 93, etc. 



proterandrous, maturing and shedding pollen before the stigma of the 

 same flower is receptive, 86. 



proterogynous, having the stigma ready for pollination before the pollen 

 of the same flower is shed, 86. 



prothallium (;pl. prothallia), the structure arising from the germinating 

 spore of vascular cryptogams and bearing the organs of reproduction. 

 The term is also extended to the homologous body in phanerogams, 

 97, 132, 140, 143, 146, 151. 



prothallus (jpi. prothalW), see prothallium. 



protonema, the algar-like filamentous structure produced by mosses in 

 germination and also, under favorable conditions, formed by their 

 stem, leaves, etc. It gives rise by budding to the leafy plant, 97, 124, 

 129, 150. 



protophloem, the first formed elements of the phloem, often persisting in 

 an^mbryonic or undeveloped condition, 45. 



protoplasm, the proteinaceous living substance of cells. 



pubescent, covered with fine, soft hairs, 58. 



pyrenoid, a proteid body with starchy envelope, occurring chiefly in the 

 chlorophyll bodies of various algse, 101. 



raceme, a simple indeterminate inflorescence in which the pedicellate 



flowers are arranged along an elongated axis. 

 radical, apparently arising from the root, 58. 

 radicle, the embryonic root at the lower extremity of the caulicle ; the 



root of seedlings, 2, 3. See caulicle. 



