214 FLOWERS A.ND THEIR WORK. 



it. Is this end part of the style the only part capable of receiving 

 pollen? Open young flowers (with the same precautions as before) 

 and remove the upper part of the style, cutting just below the tuft of 

 hairs ; cover some of these stigmaless flowers with small bags, and 

 leave others exposed. Does this affect the result? To meet the 

 objection that the removal of the stigma causes injury which might 

 account for the result, try the effect of opening some young flowers 

 and covering the top of the style with a small bit of plasticine. 



243. Pollination, The foregoing experiments show that 

 ripe seeds are not produced unless pollen conies into contact 

 with the upper part of the style that is, unless pollination 

 occurs. Will pollen from the anthers of the same flower 

 suffice, or must the pollen come from another flower ? 



(a) Cover a young unopened flower with a paper or muslin bag, and 

 see whether seeds are produced. Treat several flowers in this way, so 

 as to have a number of results on which to base your inferences. 



(6) Place pollen on the stigmas of newly opened flowers, using a fine 

 brush ; dip the brush into boiling water before using it again each 

 time (to kill any pollen left on it). In some cases (A) place on the 

 stigma pollen from the anthers of the same flower ; in others (B) bring 

 the pollen from another flower on the same plant ; in others (0) bring 

 it from a flower on another plant. In the two latter cases (B and C) 

 the flower's own anthers must be removed before they have opened. 



Simple experiments like these show that the Broad Bean can be 

 self-pollinated (Art. 246), although self-pollination does not seem to 

 occur so freely in this plant as in various other cultivated plants of the 

 Bean family (Sweet Pea, Garden Pea, etc.). In the latter plants, in 

 fact, pollination regularly occurs before the flower-bud opens, so that 

 abundant seed is set in the entire absence of insect- visitors. 



244. The Essential Organs. It is now obvious that the 

 only parts of the flower directly concerned in, and essential 

 to, seed-production are the stamens and the pistil. The 

 lowest seed-plants (e.g. Pine, Larch, Tew, Cycads) have their 

 young seeds exposed (on flat scales in most cases) to the air, 

 instead of being formed within a closed chamber or seed- 

 vessel, as in the Bean ; and the stalks of the stamens cannot 

 be considered as essential (they remain undeveloped in some 

 plants). The essential structures appear, therefore, to be the 

 anthers and the " young seeds." We know that in the Bean, 

 as in other seed-plants, these "young seeds " do not develop 

 into mature seeds, but perish like the rest of the flower, 

 unless pollen-grains are placed on the stigma. 



