326 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



over the Iris rhizomes. This quantity was gradually increased on the 

 remaining beds, so that to the last bed a maximum dose of thirty kilos 

 of marl and fifteen of magnesite was applied. 



It soon became evident that there was a marked difference between 

 the formation of new roots emitted by the rhizomes planted on the 

 prepared beds and those planted in our ordinary soil. In the latter case 

 roots were forming slowly and sparingly, whereas on the marl and 

 magnesite many more new roots were developing which also grew much 

 faster. The difference in leaf-growth in the spring also became most 

 strongly marked, and I never saw finer and healthier specimens of 

 Oncocycli than my treated plants became in the course of the spring and 

 summer of 1901. 



The experiments also showed that in my Haarlem soil (moist, well- 

 enriched sand) there was no difference in the growth made by plants in 

 beds to which the maximum dose (thirty kilos of marl and fifteen kilos 

 of magnesite) had been added from those on the bed with twenty kilos 

 of marl and nine of magnesite, but there was a marked difference in the 

 luxuriant growth of the Irises on the beds, with the maximum dose and 

 on the first bed, which contained only five kilos of marl and two of 

 masrnesite. 



The size and quality of the rhizomes grown on the marl and mag- 

 nesite, when lifted in July, fully corresponded with the fine leaf -growth 

 the plants had made, and I then felt confident that a very great stride 

 had been made forward on the road to success. On our ever-moist Dutch 

 soil I had found it necessary to take up the rhizomes of the Oncocyclus 

 Irises every year after the growth is finished in July, for if we do not 

 do so the moist subsoil causes the rhizomes to start growing again at once, 

 so that when winter sets in the plants have tender young shoots from 

 three to four inches long, and these inevitably fall a prey to frost or get 

 damped ofT if the winter is moist and misty. I now wanted to find out 

 how these treated Irises which had made such a surprisingly fine growth 

 would behave if I left them untouched, as, of course, the value of the 

 Oncocycli as garden plants would be so much greater if one could leave 

 them out all the year round, like the ordinary classes of garden Irises. 

 The best three beds with the marl and magnesite (each bed containing 

 about fourteen different species) were consequently left untouched, and 

 the unexpected result has been that, although the rhizomes showed a 

 little leaf -growth in the autumn, which is natural to them, they passed 

 through this last (severe) winter splendidly, and these plants are now in 

 a highly satisfactory condition. Also the rhizomes grown on the marl 

 and magnesite, which had been taken up in July and replanted last 

 November, although, of course, in development much behind the 

 untouched ones, are all in a very good condition. I do not, of course, 

 pretend that my experiments, which only cover such a comparatively 

 short time, have proved that all the difficulties to be surmounted in the 

 cultivation of the Oncocyclus group of Irises have been overcome, but, 

 whilst it is quite certain that these Irises cannot exist where there is 

 not an abundance of lime and magnesia in store for them, it is equally 

 certain that they can be made to flourish if these two substances are 

 supplied in due proportion. 



