‘Nothing is a better lesson in the knowledge of plants,’ says Miss Jekyll, ‘than to sit down in front of them, and handle them, and look them over just as carefully as possible; and in no way can such study be more pleasantly or conveniently carried on than by taking a light seat to the rock wall and giving plenty of time to each kind of little plant, examining it closely, and asking oneself and it, Why this? and Why that? especially if the first glance show two tufts, one with a better appearance than the other; not to stir from the place until one has found out why and how it is done, and all about it. Of course a friend who has already gone through it all can help on the lesson more quickly, but I doubt whether it is not best to do it all for oneself.’ That is excellent gardening advice, and you can apply it to whatever you are trying to do, whether it is a rock wall or a patch of Mustard and Cress. We must end this chapter with a short list of things we hope you will never allow in your rock garden, and as they are all to be seen here and there, you need not say that the advice is unnecessary. Coloured glass balls, for instance! We assure you that, especially in Germany, there are many people who think coloured glass balls beautiful objects in a garden. Others like bits of quartz, and in cottage gardens you may see sea-shells and broken glass. Then, persons who ought to know better will make a grimy erection with clinkers or broken bricks, and a home for Slugs and Woodlice with a rotting tree-stump. You must do none of these things. If you live where you can easily get stone, have a rock garden in some form, even if it is only an edging of stones to your herbaceous border, and grow some of the plants we have told you of amongst them. If you live where your walls are of brick, you may still get some plants established on them. For instance, where weeds have established themselves, you can remove them, stuff in a little good soil, and sow a few seeds of Snapdragon or Wallflower. Old brick walls make beautiful wall-gardens, and when the builder is not looking you can help on the process in a new one with a chisel, a little fine moist soil, and a few roots or seeds. CHAPTER XI DIFFICULT AND SHADY GARDENS