PLATE XXH— PRIMROSE (Primula vulgaris) and HEATH (Erica). 



Primrose. 



The Primrose might be dismissed with the convenient expression, "too well known to need description;" but, although certainly 

 known, it by no means follows that it is generally understood and appreciated, for in it there is to be seen a wonderful adaptation of 

 means to ends, which Darwin was the first thoroughly to appreciate and to explain. If the flowers are examined on several different 

 plants it will be found that they vary: those on one plant having the knob-headed stigma at the entrance to the corolla-tube, and those 

 on another having the stamens in that position. These two different forms of flowers are respectively called Long-styled and Short- 

 styled. A glance at Fig. 2 will show that an insect visiting the long-styled flower, and thrusting its proboscis down the tube, will 

 carry away pollen so placed that, on visiting a short-styled flower, it will come in contact with the stigma, and thus ensure cross- 

 fertilisation. Reversing the order of its visit, from short-styled to long-styled, the insect would still produce the same effect 



The Pollen-grains, too (Fig. 4), are adapted for their respective duties. In the long-styled flower they are smallest because they 

 are intended to be transferred to the stigma of the short-styled flower, and so have to produce a shorter pollen-tube than the other. 



The Primrose appears in early spring (Primula, from Lat primus, first) at a time when insect life is still scarce ; and yet so perfect is 

 the adaptation of its various parts to secure cross-fertilisation — with the minimum of waste, so attractive is its flower and scent, and so 

 well-chosen its situation on sloping bank or sheltered glade that it not only manages to thrive, but often overspreads the hedge-bank 

 with its blossoms like so many golden stars. 



Fig. 1. Form and Habit of the plant 



The wrinkled Leaves stand out from the base in radiating fashion, and the Flowers also radiate from a centre, 

 having long flower-stalks. Here the Umbel is sessile, but in Cowslip it is stalked. 



FigS. 2 and 3. Slit up a Long-styled and Short-styled form of flower from the base, and compare them. 

 Stigma of one about the same height as the Anthers of another. 



Fig. 4. Dust pollen on slides from the Anthers of the respective flowers, and observe different relative size in each case. 



Fig. 5. Vertical section of Ovary, showing a free central column, to which the Ovules are attached. 



Fig. 6. Fruit — met with in July. 



Capsule of five valves opening by ten teeth, and containing numerous Seeds. 



Fig. 7. Seed halved. 



Seed-cover raised into little elevations. 

 Embryo surrounded by Endosperm. 



CLASSIFICATION. 



Class. — Dicotyledon. 



Division. — Gamopetalae. 



Calyx and Corolla present. 

 Petals, united. 



Order. — Primulacese. 



Corolla, regular. 



Stamens, attached to corolla-tube, opposite petals. 



Ovary, superior, one-chambered. 



Ovules, numerous ; Placentation, free-central. 



Fruit, capsular. 



Seed with endosperm. 



Heath. 



Heath is sufficiently common to give its name to large tracts of country where it protects the surface of otherwise barren wastes. 

 It flowers during the summer months, when its modest bloom delights the eye and 



"sheds beauty o'er the lonely moor." 



Heather (Calluna) blooms in autumn, and the flower differs from that of Heath (Erica), principally in the Calyx being longer than the 

 Corolla, and having four bracts at its base. Rhododendron is a well-known allied ornamental shrub, with large and showy flowers. 



Fig. 8. Form and Habit of the plant 



The Stem is upright and much branched. The Leaves are in close-set whorls of four, and the Flowers are 

 arranged in crowded racemes. 



FigS. 9 and 10. Flower entire and in section. 

 Calyx of four sepals and coloured. 

 Corolla is bell-shaped, with four broad lobes. 



Stamens, eight ; anthers outside of corolla tube, and each opening by two pores. 

 Carpels, four, un'.ted, with Style projecting beyond anthers. 



Fig. 11. Flower of Rhododendron in section. 



Calyx, represented only by minute teeth. 

 Corolla of five lobes, deciduous and irregular. 

 Stamens, ten. 

 Carpels, five, united. 



Diagram II.— Calyx of four Sepals. 



Corolla of four united Petals. 



Andrcecium of eight Stamens, four opposite to sepals and four opposite to petals. 



Gyncecium of four united Carpels. 



Fig. 12. Transverse section of Ovary. 



The Ovary is divided into four chambers, with numerous Ovules in each, springing from the Axis. 



Fig. 13. Fruit of Rhododendron — a Capsule. 



The Carpels separate in the form of five Valves, the sides of which are lormed by the split septa. In Heather 

 the Capsule splits similarly, but is four-valved ; while in Heath the splitting of the valves takes place along the 

 midrib cf each carpellary leaf. 



