NORTH SIDE OF THE ROCK GARDEN 215 



its more vigorous variety hirsuta, with excellent ef- 

 fect. One of the most valuable plants for covering 

 a lai'ge space on a northern slope is Polygonum vac- 

 cinifolium. It is quite prostrate and flowers in late 

 summer and autumn. It grows very quickly, the 

 stems rooting in the ground, and no small plants 

 should be put near it. It flowers best in a rather poor 

 soil and open situation. It should be planted in 

 spring and not disturbed afterwards. Space also is 

 needed for Dryas octopetala, a lime-loving plant, 

 which grows Into a large prostrate mass, bearing 

 white blossoms rather like those of a strawberry 

 throughout the summer. Many of the smaller Drabas 

 do well on the north side, especially D. Aizoon, D. 

 aizoides, and D. brunlsefolla. Of these D. Aizoon, 

 a native plant and easily raised from seed. Is the best. 

 It grows in little rosettes with a head of yellow flowers 

 rising from the centre of them. It is quite easy, but 

 does not like a hot sun. The other two are more 

 mossy in growth and cover a larger space. Another 

 little crucifer with yellow flowers that thrives on the 

 north side is Morisia hypogsea. It blossoms very 

 early In the spring and should be planted In a deep 

 crevice, between rocks. When it has formed several 

 crowns it should be divided, and replanted in fresh 

 soil just after flowering. It is a plant to associate with 

 the smaller Alpine Primulas, most of which like a 

 north-west aspect and the same deep crevices. The 

 best of all these, perhaps, Is Primula pubescens alba 

 (or nivalis), a small but vigorous plant with pure 



