POLLEN. 



**** Four pores. 



a. Pores on the equator : Pistacia tere- 

 binthus, Campanula rotundifolia, &c. 



b. Pores not equatorial : Passijlora ker- 

 mesina, Impatiens Balsamina (PI. 32. 

 fig. 21), Noli-me-tangere. 



***** More than four pores, 

 t Distributed regularly. 



a. On the equator : Alnus glutinosa, XJlmus 

 campestris, CoUomia linearis^ Campa- 

 nula Speculum. 



b. All over the grains : Basella alba (PI. 

 32. fig. 19). 



tt Scattered irregularly. 



a. Outer coat slightly granular : many 

 Nyctagineae, Convolvulaceae, Chenopo- 

 diacese, Alsinese, Alisma Plantago (PI. 

 32. fig. 10), Plantago lanceolata. Kibes 

 nigrum, Cactus Opuntia, &c. 



b. Outer coat granular and spiny : Cucur- 

 bita Pepo (with hds, PI. 32. fig. 22), 

 Malvacejfi (PI. 32. fig. 26). 



c. Outer coat with cell-like reticulations : 

 Polygonium amphibium, Persicaria, 

 Cobcea scandens. 



Compound porous forms occur in some of 

 the Onagracese, in Drimys Winteri, w^here 

 four grains are conjoined tetrahedrally. In the 

 Mimoseae groups of eight or sixteen (PI. 32. 

 fig. 25) occur in various forms. In Lesche- 

 naultia formosa the grains are quaternate, 

 lying in one plane. 



D. Outer coat with both furrows and pores. 



* Grains rounded or depressed, with 

 three depressions, each with a pore : 

 most Dipsacese and Geraniacese 

 (sometimes only two occur, PI. 32. 

 fig. 22). 



** Three furrows and three pores. 



a. Outer coat granular; a very common 

 form among Dicotyledons. 



b. Outer coat spiny : most Compositee. 



c. Outer coat with cell-like reticulations ; 

 rare : Syringa vulgaris, Ligustrum vul- 

 gare, Grewia occidentalis, and other 

 species. 



*** Outer coat with more than three 

 furrows, each wdth a pore. Some- 

 times abnormally, instead of three, 

 but normally in most of the Boragi- 

 nacese and Polygalaceae. 



[ 520 ] POLYBOTRYA. 



**** g-^ ^^ j^jjjg furrows, three con- 

 taining a pore : Lythracese, Melasto- 

 macese, Combretaceae. 



***** Three or four furrows, with six 

 or eight papillae : Neurada procum- 

 bens, &c. 



****** Three furrows and three papillae 

 not in the furrows : Carolinea cam- 

 pestris, &c. 



Related compound forms occur in the 

 Ericaceae and Epacridaceae, where the grains 

 are tetrahedrally arranged (PI. 32. fig. 17). 

 Other aberrant forms occur in which the 

 single grains are cubic or dodecahedral ; and 

 in the Cichoraceae, polyhedral forms of com- 

 plicated character are common (PL 32. figs. 

 16, 27, 28). 



Mature pollen-grains should be observed 

 dry (as opake and transparent objects), and 

 in water; in some cases, in oil; treatment 

 with acids is also useful in making out struc- 

 ture. In observing the development of pol- 

 len, it is necessary to wet the object with a 

 solution of sugar or gum, otherwise the ap- 

 pearances are altogether changed through 

 endosmotic action. 



BiBL. Mohl, Bau u. Form. d. Pollenkbr- 

 ner, Bern, 183'^ (transl. in Ann. des Sc. nat. 

 2 ser. iii.) ; Purkinje, De cellulis antheris, 

 Sfc, Vratislav. 1830; Fritzsche, Beitr. z. 

 Kenntn. der Pollen, 1832; Hassall, Ann. 

 Nat. Hist. viii. p. 92; ix. p. 93 and 544. 

 Mohl's work contains an abstract of the 

 literature up to his date ; since that time 

 notices on the development have been jjub- 

 lished by Nageli, Entwick. des Pollens, Zu- 

 rich, 1842, and his papers on Cell-formation 

 translated in Ray Society's Vols, for 1846 

 and 1847; Hofmeister, Botanische Zeitung, 

 vi. 1848; Gieswald, Linncea, xxv. p. 81 

 (1852); Schacht (Coniferae), Beitrag. z. 

 Botanik. Berlin, 1854. 



POLYACTIS. See Botrytis. 



POLYARTHRA, Ehr.— Agenus of Rota- 

 toria, of the family Hydatinaea. 



Char. Eye single, cervical ; foot absent ; 

 body with six cirrhi or fins on each side. 



Jaws each with a single tooth. 



P. platyptera (PL 35. fig. 19). Body 

 ovato-subquadrate, fins ensiform serrate. 

 Aquatic; length 1-190". 



P. trigla. Fins setaceous. Aquatic ; 

 length 1-190". 



BiBL. Ehrenberg, Infus. p. 440. 



POLYBOTRYA, Humb. — A genus of 

 Acrosticheae (Polypodaeous Ferns). Exotic. 



