February 



IRISH GARDENING. 



21 



beauty enhanced by a central bunch of red anthers. 

 H. Heiiryi is also gfood, attaining- three feet in height, 

 and producing^ large yellow flowers. Hypericums should 

 have a sunny position in fairly good soil. 



The shrubby Cinquefoils are eminently suitable for 

 this purpose, and can now be had in some variety. 

 Potentilla Friedrichseni — a garden hybrid — is extremely 

 beautiful, of erect habit, and bearing numerous soft 

 yellow flowers throughout the summer. P. fmficosa, 

 fairly well known, bears yellow flowers freely, while the 

 variety P. f. humilis is of dwarfer habit and cqualh- 

 floriferous. P. frut. arbuscula, seeds of which were 

 received at Glasnevin from Sikkim, gives promise of 

 being useful. P. (favurica is quite low growing, with 

 yellow flowers, while P. sali'soviaiia is a distinct plant of 

 looser growth bearing somewhat hairy leaves, whitish 

 underneath, and producing fine white flowers in summer. 

 P. micrandra., of uncertain origin, resembles the fruticosa 

 set. 



Peroz'skia atriplicifolia, a shrub of the salvia family, is 

 distinct and beautiful. The general appearance of this 

 plant is decidedly silvery, the effect being enhanced in 

 late summer by the spikes of violet-blue flowers ; a sunnv 

 aspect in loamy soil is suitable. Coprosma acerosa^ a 

 twiggy prostrate New Zealand plant, lends variety, and 

 is Interesting when bearing quantities of bluish smoke- 

 coloured berries. 



A large number of shrubby veronicas may be used in 

 the rock garden, while the members of the heath family 

 are a host in themselves. Heaths generally do not 

 flourish where lime is present in the soil, but Erica carnea, 

 one of the most beautiful spring flowering plants, is an 

 exception, and grows freely In loam containing lime. 



The list of suitable subjects is not exhausted, but 

 enough may have been mentioned to show the wealth 

 of material available. 



Inoculation of Leguminous Crops. 



TH E question as to the beneficial use of inoculation 

 by artificial cultures of bacteria in the case of 

 leguminous crops has been acutely raised by 

 the publication of the results of Mr. F. G. Chittenden's 

 experiments at Wisley during the past season. .As 

 doubtless our readers know the latest and most ex- 

 tensively boomed culture is the " nitro-bacterine" of 

 Professor Bottomley, made up in five shilling packages 

 and distributed by an agenc)' cc>ntrolled by Mr. Stead 

 of the Review of Revie-.i's. This was the "brand" of 

 culture used in the Wisley experiments, and the object of 

 the experiments was to find out if its use in an ordinary 

 garden soil was attended with any distinct advantage to 

 the crop. 



Now, it has been known for a very long time that a 

 leguminous crop, such as peas, beans, clovers, &c., 

 leaves the soil distinctly richer in nitrogenous matter 

 than it was before it carried the crop. Why is this? 

 The answer forms one of the minor romances of science. 

 The experiments of Boussingault in 1854, and those of 

 Lawes and Gilbert later, demonstrated that the plant's 

 only source of nitrogen was the soil, and that apparently 

 this element was always taken up by the roots in a com- 

 bined form. Twelve years after, Hellriegal and Walfarth 



discovered, however, that these leguminous crops could 

 make use of the free nitrogen gas of the air, but only by 

 those plants that were provided with " nodules." The 

 nodules or swellings on the roots of leguminous plants are 

 and have been for ages familiar to gardeners, but until 

 about this time their true significance was never even 

 guessed. It was further discovered that, if before the seed 

 were planted, the soil was sterilised so as to destroy all Its 

 microscopical life, the plants failed to produce nodules, 

 and if in addition to sterilisation the soil was deficient in 

 nitrogen the plants would eventually die of nitrogen star- 

 vation. It was found, moreover, if either crushed nodules 

 or a little fresh garden soil were washed in water and the 

 washings mixed with the sterilised soil, the roots would 

 certainly form nodules and the plants flourish even if the 

 soil was devoid of nitrogen compounds. Marshall 

 Ward, in 1887, from a series of experiments he had 

 carried out, drew the inference that the root nodules 

 contained living bacteria, and that it was owing to the 

 vital activity of these that the crop was able to obtain 

 its supplies of nitrogen direct from the air. This 

 announcement was followed in 1888 by the actual dis- 

 covery and isolation of a specific nodule bacterium by 

 Beijerinck, and so far the problem was solved. Exactly 

 how the nitrogen is fixed Is, however, still a biological 

 puzzle, although recent experiments of Greig Smith 

 (1907) show that in alkaline artificial cultures containing 

 sugars a nitrogenous slime is formed, which he assumes 

 to be the substance formed in the nodules and made use 

 of by the leguminous plant. 



It must be remembered that inoculation simply 

 supplies the living nitrogen-fixing germs to the soil, and 

 therefore, if the right kinds of germs are there already, 

 little advantage is likely to follow the introduction of an 

 additional supply, as given favourable soil conditions 

 the germs are able to multiph'and spread at an amazing 

 rate. On the other hand, if the soil is unfavourable to 

 the life of these particular germs, inoculation, obviouslv, 

 can be of very little use. 



To enable a leguminous crop to fix the maximum 

 amount of nitrogen from the air, first nodule-forming 

 bacteria must be present in the soil, and second the con- 

 dition of the soil must be favourable to the development 

 of the germs. Now, this particular soil condition is 

 exactly the condition that favours the production of 

 heavy and healthy crops — that is to say, the soil must be 

 (i) well-drained,elseit will tend to be sour, and any acidity 

 is detrimental to bacteria life, (2) thoroughly tilled so as 

 to enable it to hold an abundance of moisture and air, 

 (3) sufficiently supplied with available compounds of 

 phosphoric acid and potash. 



It is a matter of experience that most, if not indeed all, 

 cultivated garden soils in this country contain already 

 these particular nodule-forming germs, and one would 

 naturally assume that inoculation would be entirely 

 superfluous in such cases. 



Let us now turn to the Wisley experiments and their 

 results. These experiments were planned and carried 

 out with great care. There were 24 equal-sized plots, 

 12 on deeply, well-cultivated soil and 12 on fallow land 

 with shallow cultivation. The soil on analysis showed 

 that It was not lacking in any of the chemical substances 

 essential for bacterial growth and development ; but to 

 make the experiment all the more thorough some of 



