Tropaeolum minus.

The flowers are proterandrous, and are manifestly adapted for cross-fertilisation by insects, as shown by Sprengel and Delpino.  Twelve flowers on some plants growing out of doors were crossed with pollen from a distinct plant and produced eleven capsules, containing altogether twenty-four good seeds.  Eighteen flowers were fertilised with their own pollen and produced only eleven capsules, containing twenty-two good seeds; so that a much larger proportion of the crossed than of the self-fertilised flowers produced capsules, and the crossed capsules contained rather more seed than the self-fertilised in the ratio of 100 to 92.  The seeds from the self-fertilised capsules were however the heavier of the two, in the ratio of 100 to 87.

Seeds in an equal state of germination were planted on the opposite sides of four pots, but only the two tallest plants on each side of each pot were measured to the tops of their stems.  The pots were placed in the greenhouse, and the plants trained up sticks, so that they ascended to an unusual height.  In three of the pots the crossed plants flowered first, but in the fourth at the same time with the self-fertilised.  When the seedlings were between 6 and 7 inches in height, the crossed began to show a slight advantage over their opponents.  When grown to a considerable height the eight tallest crossed plants averaged 44.43, and the eight tallest self-fertilised plants 37.34 inches, or as 100 to 84.  When their growth was completed they were again measured, as shown in Table 5/50.

Table 5/50.  Tropaeolum minus.

Heights of plants measured in inches.

Column 1:  Number (Name) of Pot.

Column 2:  Crossed Plants.

Column 3:  Self-fertilised Plants.

Pot 1 :  65 :  31. 
Pot 1 :  50 :  45.

Pot 2 :  69 :  42. 
Pot 2 :  35 :  45.

Pot 3 :  70 :  50 4/8. 
Pot 3 :  59 4/8 :  55 4/8.

Pot 4 :  61 4/8 :  37 4/8. 
Pot 4 :  57 4/8 :  61 4/8.

Total :  467.5 :  368.0.

The eight tallest crossed plants now averaged 58.43, and the eight tallest self-fertilised plants 46 inches in height, or as 100 to 79.

There was also a great difference in the fertility of the two lots which were left uncovered in the greenhouse.  On the 17th of September the capsules from all the plants were gathered, and the seeds counted.  The crossed plants yielded 243, whilst the same number of self-fertilised plants yielded only 155 seeds, or as 100 to 64.

Limnanthes douglasii.