Poitsea 



(219) 



Pollination 



kernel of the fruit that is the poisonous part. 

 Among British plants the Hemlock, Fool's Parsley, 

 White Bryony, Deadly Nightshade, Thorn Apple, 

 Foxglove.'and Monkshood are all very poisonous. 

 The roots of the latter, much like Horseradish in 

 appearance, almost always prove fatal to the 

 eater ; the poison is aconitine. 



Vr'jvtable poisons may be irritant, narcotic, or 

 narcotico-irritant, chiefly the two latter. Hydro- 

 cyanic acid, formerly known as prussic acid, 

 belongs to the second class. It can be distilled 

 from Almond kernels, but is now generally pro- 

 duced chemically. Under narcotic poisons must 

 also be included Opium and Henbane. Among 

 irritant poisons Colocynth, Croton-oil, Elaterium, 

 Gamboge, and Savin are the chief, while into the 

 class of narcotico-irritants come the poisonous 

 properties of the British plants mentioned in 

 the preceding paragraph, as well as Tobacco, 

 Strychnos Nnx-vomica, Laburnum (bark and seeds), 

 Yew (leaves), Hellebore, and most species of 

 Fungi. 



Many vegetable poisons are valuable medicinally 

 when administered in small doses and in certain 

 combinations, but in all cases their use should be 

 left to the direction of a medical man, and their 

 preparation to the dispenser. 



POIT^EA. 



Dwarf-growing stove shrubs (ord. Leguminosre). 

 Propagation, by cuttings in sand over bottom heat. 

 Soil, loam, with plenty of coarse sand. 



Principal Species : 

 galegoides, 1', Jc., rosy pur. 



POLANISIA. (CLEOME.) 



Hardy annuals {ord. Capparideaj). Propagation, 

 'by seeds sown under glass in April and planted in 

 my ordinary garden soil at the end of May. 



Principal Species : 



Cheliclonii, l\' , Jo., ro. uniglandulosa, IV, Je., 



dodeoandra, It', Je., wh. reddish yel. 



graveoleus, If, Je., pk. viscosa, 2', Je., yel. 



POLEMONIUM. 



Description. Pretty, hardy or half-hardy, annual 

 or perennial herbs (ord. Polemoniaceaa), which 

 make a pleasing effect in the border or rock garden. 

 The variegated-leaved form of ceeruleum is often 

 used as an edging, for which purpose the flower 

 buds should be pinched off as they show. 



Propagation. The perennials by division in 

 spring or early autumn, and by seeds in spring ; 

 the annuals by seeds at the same season. 



Soil. Good rich loam for the border plants, but a 

 lighter one for the Alpine species. 



Principal Species and Varieties : 



ccKruleum, '2', Je., bl. confertum, G", sum., bl. 



Jacob's Ladder, Greek melitum, wh. 



Valerian, Charity. flavum, 2' to 3', Aug., 



album, wh., foliage pale yel. 

 various, Ivs. gm., wh. humile, G", Jy., hi. 



- campaiiulntiim, Ap., reptans, 6", Ap., bl. 



My., bright hi. Richardsoni, 1', sum., 



dissectum (ni/n. sibiri- pur. bl. (//. humilis 

 cum). Kichardsoni of some). 



J'oiso/i Siinnii'li (see Illnis n-nenata). 



1'ii'irrra (see fniiihretiim'). 



Poke \\'<-cd (HV PIn/tolacea). 



Polar Plant (se<: Silphium laciniatum). 



Other Species and Hybrid : 



flavo-ccuruleum. 3' to 4', pauciflorum, I-!', sum., 



sum., wh., hybrid. yel., red. 



himalayauum, 1' sum., 



HI., bl. 



POLIANTHES. (TUBEROSE.) 

 Greenhouse, bulbous plants (ord. Amaryllideae), 

 They will flower out of doors in a favoured climate 

 provided the soil be light and sandy. Propagation, 

 which is rarely resorted to in this country, is by 

 offsets. Soil, mellow loam with sand. (For full 

 cultural details, see TUBEROSE.) 



Only Species and its Varieties : 



tuberosa, 3', Aug., wh. florepleno,3',Aug. ,wh, 



gracilis, 3', Aug., yel. 



POLLEN. 



The male organs of a flower are the stamens and 

 anthers ; the latter are essential, but the former 

 may be so reduced as to be practically absent. 

 Within each anther pollen is produced by cell 

 division, eventually becoming separate grains in 

 the majority of flowering plants ; in Orchids the 

 grains combine to form the pollen masses. An 

 anther does not burst until the pollen is ripe, i.e. 

 in 'a suitable condition to cause fertilisation when 

 applied to a receptive stigma. Pollen varies a 

 little in colour, but is most familiar as a yellow 

 or greenish yellow powder ; in many Liliums it 

 assumes a brownish tint, while in Scillas it is 

 bluish. Though varying much in shape and size, 

 pollen grains are nearly all furnished with two 

 coats or skins, the outer (extine) and the inner 

 (intine), the latter being very elastic. When a 

 grain is placed upon a ripe stigma, there are 

 openings in the outer coat, through which the 

 inner one forms an elongated tube that grows down 

 through the style into the ovary, conducting the 

 most important part of the grain contents, the 

 nucleus, through the micropyle of an ovule to the 

 embryo. 



POLLIA. 



Stove herbaceous perennials (ord. Commelin- 

 aceae). Propagation, by division or by seeds. 

 Soil, loam, leaf mould, and sand. 



Principal Species : 



crispata, sum., trailer, bl. (sy n. Aneilema crispata). 



POLLINATION. 



The transfer of pollen from anther to stigma is 

 known technically as pollination, and it is effected 

 by Nature in many wonderful ways. In the 

 majority of flowers the pollen is not ripe at the 

 same time as the stigma is receptive, but there 

 may be ripe pollen and receptive stigmas on the 

 same plant and on the same inflorescence ; conse- 

 quently, unless by the help of wind, insect, or other 

 outside agency, pollination cannot take place. This 

 gives a reason for pollen distribution by artificial 

 means, such as a dry hand, hare's or rabbit's tail, 

 or a camel hair brush, to secure a good " set " on 

 Peaches, Nectarines, Vines, etc., grown under glass. 

 Melons form another illustration of the need for 

 artificial pollination when insects have not access 

 to the flowers, but in this case the male and female 

 organs are not found in the same flower. Herma- 

 phrodite flowers in which the pollen is ripe before 

 the stigma is receptive are called Protandrous, while 

 those in which the stigma is receptive before the 

 pollen is ripe are known as Protogynous Protandry 



