Tenth leaf or leaflet vein angle
These features refer to the tenth leaf stage. The tenth leaf is the tenth true leaf produced after the cotyledons. On seedlings with alternate or spirally arranged leaves it is just simply the tenth leaf produced. On seedlings with opposite leaves it is one of the leaves in the fifth pair of true leaves produced. On seedlings with whorled leaves it will be one of the leaves in the appropriate whorl; e.g. if there are four leaves in each whorl then the tenth leaf will be one of the leaves in the third whorl.
This is the angle between the midrib and the lateral vein, measured from the midrib, on the leaf blade (or leaflet blade in the case of compound leaves). A special technique is used for curved lateral veins. The vein angle is measured in the following way. Decide which lateral vein to study. Go to the next vein above and draw a line from its base and at right angles to the midrib until it intersects the vein in question. Draw a line from this point to the base of the vein in question. The vein angle is the angle between this line and the midrib. (figs a,b)