Plants in Relation to Man 493 



a long, narrow tube containing the honey, which can be reached 

 only by the long proboscis of the bumblebee. Orchids of cer- 

 tain kinds yield their nectar only to moths with unusually long 

 proboscides. The snapdragon opens its nectary tube only to 

 an insect of such weight as the bee, thus excluding smaller 

 insects and especially ants, which merely consume the nectar. 

 The throats or tubes of many flowers are provided with hairs 

 or bristles to exclude unbidden guests. 



237. Cross-pollination and variation. A plant which is 

 the product of the pollen from one plant and of the ovule from 

 another of the same species, or from another plant of a different 

 variety of the same species, can never be a " chip of the old 

 block." It may repeat certain characteristics of the parent 

 plants, but it is a new variety, with striking differences from, 

 however much it in general resembles, its kind. As is well 

 known, plants combining the excellent characters of parent 

 plants grow more vigorously and rapidly, have greater strength, 

 health, and productiveness than the ancestral plants. From 

 man's point of view such varieties are valuable ; and to pro- 

 duce them is one of the chief aims in plant improvement. 



Exercise. That individual varieties occur in any kind of plant 

 may be interestingly demonstrated. In soil of the kind most suitable 

 for the selected plant, and supplied with the best degree of moisture, 

 warmth, and light, plant at the same depth and with the same soil 

 allotment fifteen to twenty seeds of the same crop or plant, selected 

 for their equality in all essential respects. Such seeds as corn, pump- 

 kin, peas, and beans will do well. The result is instructive. No two 

 grow at the same rate, with the same vigor, strength, and health, and if 

 the plants were observed until they matured, corresponding differences 

 would be found. These points are fundamental in the selection of seed. 



Exercise : Relation of floral structures to insect-pollination. Ob- 

 serve the position of the nectar relative to the stamens with their 

 anthers, and to the stigmas. The nectar is found in different places 

 in different kinds of flowers, in some on the base of the stamens, in 

 others on certain parts of the petals, and still elsewhere in others. 

 But it is so located that insects getting it are brought into contact 

 with the anthers and stigmas. 



