Often the plants produce one complete layer of radial spines and a second layer in the uppermost part of the areole only. Similarly, it often occurs that the upper radial spines are more densely set. This gives the impression of bundled radial spines in the upper part of the areole. Upper radial spines may also differ in colour, and they are often thinner and longer than the lateral and lower ones. The description concerns the number,direction and position of the radial spines (see Fig. 17).
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