72 Commercial Gardening 



Natural Groups. In the following pages the various vegetable crops 

 are described chiefly in alphabetical order for the sake of convenient refer- 

 ence. It may be as well, however, to set them out in their natural groups 

 as far as possible, so that one may see at a glance how the principles of 

 rotation may be applied. 



I. BEASSICAS or CABBAGE CROPS. Broccoli, Borecole or Kale, Brussels 

 Sprouts, Cabbage (including Savoy), Cauliflower, Kohl-rabi, Sea- 

 kale, Radish, Turnip. These are all subject to attack from the 

 " Club-root " fungus (Plasmodiophora brassicce). 



II. LEGUMINOUS or NITROGENOUS CROPS. Beans (Broad, Dwarf or 

 French, and Runners) and Peas. The roots of these crops 

 increase the stores of nitrogen in the soil by the bacterial 

 nodules on their roots. See Vol. I, p. 125. 



III. UMBELLIFEROUS CROPS. Carrots, Parsnips, Celery, Parsley. 



IV. SOLANACEOUS CROPS. Potatoes, Tomatoes. 



V. BULBOUS or ALLIACEOUS CROPS. Onion, Leek, Garlic, Shallot. 

 VI. COMPOSITE CROPS. Artichokes (Jerusalem and Globe), Lettuce, 



Salsafy, Scorzonera, Chicory, Cardoon. 



VII. MISCELLANEOUS. Beetroot, Spinach, Rhubarb, Vegetable Marrow, 

 Asparagus, &c. 



Crops belonging to the same family have somewhat similar natures, and 

 are as a rule subject to the same diseases and pests. Their roots have a 

 similar effect on the soil, and it is possible that so-called "soil sickness" 

 is due to the superabundance of certain secretions from the roots. Con- 

 sequently when plants of the same nature are grown in the same soil 

 continually, without a reasonable lapse of time, their roots find themselves 

 surrounded by the injurious organic secretions of previous crops. And yet, 

 if plants of a totally different nature were put in the same soil, the secre- 

 tions (no doubt bacteria of some kind), instead of being injurious, would 

 in all probability be of great benefit to them. It is thus easy to conceive 

 a state of affairs in the soil by means of which the refuse of one crop 

 may be of use to another of a dissimilar nature. By changing the various 

 crops from one piece of land to another, therefore, not only does the ground 

 get a "change", but the new crops are likely to be in a position to make 

 use of what their predecessors threw away; in other words, one plant's 

 meat may be another plant's poison. From this it follows that it would 

 not be wise cultivation to crop soil in succession with plants belonging to 

 the same natural groups outlined above. The crops in any one group may 

 follow those in any other, thus securing a beneficial change of soil and 

 food. 



2. ARTICHOKES 



The Jerusalem Artichoke (Helianthus tuberosus).-This tuberous- 

 rooted plant is closely related to the common Sunflower, and resembles 

 it in appearance. Except in very hot seasons and in the most favoured 



