August 1, 1908 



HORTICULTURE 



129 



Notes from the Arnold Arboretum 



One of the most attractive of the late flowering 

 shrubs is the native White Alder or Sweet Pepperbush, 

 Clethra alnifolia, which is now beginning to open its 

 fragrant white flowers. In its wild state it inhabits 

 usually swamps ami the hanks of ponds or streams, but 

 in cultivation it takes kindly to drier situations and 

 grows well in partial shade. In too dry and sunny 

 situations, however, the foliage is apt to get discolored 

 by becoming infested with the red spider. If planted 

 solitary or on borders of shrubberies it rarely exceeds 

 five feet in height and forms a round dense bush 

 studded all over from the end of July to the middle of 

 August with upright white flower spikes, but if growing 

 between other shrubs it sometimes attains to ten feet in 

 height. A variety which usually remains low and flow- 

 ers several weeks later is C. alnifolia var. tomentosa 

 with longer flower spikes and pubescent foliage. A 

 pretty variety but recently discovered near Wattuppa 

 Lake, Fall River, Mass., has pinkish flowers in dense 

 spikes and has therefore been termed var. rosea; on ac- 

 count of its color it will add a pleasing variety to 

 groups of the common form. Another native species, 



Clethra acuminata, is less handsome; it forms a loosely 

 branched shrub or small tree up to fifteen feet high with 

 spreading branches bearing usually solitary spikes of 

 creamy white flowers. Very similar is the Japanese C. 

 canescens (C. barbinervis) with several larger spikes at 

 the end of the branches : it is prettier than C. acuminata, 

 but is tender in the neighborhood of Boston. 



Several of the native Spireas are now coming into 

 bloom : they all belong to the section Spiraria and have 

 the rather stiff habit of the species of this section. The 

 handsomest of them is the Hardback or Steeplebush, 

 Spiraea tomentosa, with slender spikes of pink flowers 

 and the stems and foliage densely covered with yellowish 

 brown toementum. Two other native species have 

 white or slightly pinkish flowers; these arc Spiraea alba 

 and S. latifolia, usually included under S. salicifolia, 

 but it seems more natural to use the name S. salicifolia 

 ■only tor the Old World species which is characterized 

 by light pink flowers in dense panicles. Spiraea lati- 

 folia is the species common in tin- region and has white 

 flowers slightly tinged pinkish h\ the pinkish disk and 

 stamen- and arranged in rather loose panicles broad at 

 the base. Spiraea alba is a more southern species and 

 found chiefly west of the Alleghenies, it has pure white 

 flowers in narrow panicles, narrower leaves and stiff 

 upright stems. 



The las< of the Sorbarias to bloom is Sorbaria sorbi- 

 folin var. dubia, very similar to S. sorbifolia but grow- 

 ing higher and of more spreading, less stiff habit. Also 

 Sorbaria stellipila and >'. Aitchisonii have still a few 

 belated flower clusters; the latter species has already 



«en noted in the issue of July 18 as one of the most 

 desirable of the Sorbarias. Sorbaria stellipila i 

 hies much more >. sorbifolia, but besides flowering later 

 it is of less stiff habit and has narrower and longer 

 leaflets. 



The Bittersweet, Solanum Dulcamara is now very 

 handsome with its drooping clusters of glossy scarlet 

 berries and its violet star shaped flowers which continue 

 to appear until September. It is a pretty vine for moist 

 situations and finds it- best place rambling among the 

 shrubs along streams or in other moist and partly 

 shaded situations; the foliage, however, is apt to suffer 

 from the ravages <>( insects. 



British Horticulture 



A DESTRUCTIVE POTATO DISEASE 



The ravages caused by the spread of black scab in 

 potatoes have given great concern to growers in this 

 country. The matter has lately been discussed at a 

 conference at the Board of Agriculture. The National 

 Fruit Growers' Federation who are taking up the ques- 

 tion suggested that it should be made illegal for a 

 grower to sell potatoes from a farm or holding where 

 the disease was known to exist until they had been ex- 

 amined by some duly qualified person; that potatoes 

 found diseased should be destroyed, the grower being 

 compensated from treasury funds up to half their value, 

 and that growers who plant potatoes within a period of 

 years im ground where the disease has existed must, 

 before offering the crop for sale, possess a certificate of 

 the Board of Agriculture, certifying the land to be free 

 from disease. The Board favorably received these sug- 

 gestions, and agreed to schedule black scab as a notifi- 

 able disease. They also decided to adopt a further rec- 

 ommendation for withdrawing the published leaflet 

 which stated that black scab was able to attack man- 

 gold and beet. The Board will also make investiga- 

 tions as to whether the disease was being introduced 

 into this country by means of imported seeds. At a 

 recent meeting of the Federation a speaker stated that 

 the disease is more in feet Sous from the soil than from 

 the tubers themselves, and experts asserted that it was 

 not safe to plant potatoes on land where the disease had 

 recurred for six or seven years. The important thing 

 the Board of Agriculture desire the Federation to tell 

 them was how they could determine when a crop is in- 

 fected, because there appears to be nothing to indicate 

 the presence of (he disease except in the potatoes them- 

 selves. This is a matter of extreme importance to com- 

 mercial horticulture. 



>3V. QM*&. 



