190 READINGS IN BIOLOGICAL SCIENCE 



or races as a whole, instead of contenting themselves with one or two clear- 

 cut characters. The new thing about Mendel's method was that he had 

 confined himself to studying the effects of hybridization upon single par- 

 ticular characters, and that he didn't take, as his predecessors had done, 

 only a summary view upon a whole generation of hybrids, but examined 

 each individual plant separately. 



The experiments, the laws derived from these experiments, and the splen- 

 did explanation given to them by A4endel are to-day not only the base of 

 the modern science of genetics, but belong to the fundamentals of biology 

 taught to millions of students in all parts of the world. 



Mendel had been since 1843 one of the brethren of the beautiful and 

 wealthy monastery of the Augustinians of Bruenn, at that time in Austria, 

 later in Czechoslovakia. His profession left him sufficient time, and the 

 large garden of the monastery provided space enough, for his plant hybrid- 

 izations. During the eight years from 1856 to 1864, he observed with a rare 

 patience and perseverance more than 10,000 specimens. 



In hybridization the pollen from the male plant is dusted on the pistils 

 of the female plant through which it fertilizes the ovules.* Both the pollen 

 and the ovules in the pistils carry hereditary characters which may be alike 

 in the two parents or partly or entirely different. The peas used by Mendel 

 for hybridization differed in the simplest case only by one character or, 

 better still, by a pair of characters; for instance, by the color of the flowers, 

 which was red on one parental plant and white on the other; or by the shape 

 of the seeds, which were smooth in one case and wrinkled in the other; or 

 by the color of the cotyledons, which were yellow in one pea and green 

 in the other, etc. Mendel's experiments show in all cases the result that all 

 individuals of the first generation of hybrids, the Fi generation as it is called 

 to-day, are uniform in appearance, and that moreover only one of the two 

 parental characters, the stronger or the dominant one, is shown. That means, 

 for instance, that the red color of the flowers, the smooth shape of the seeds 

 or the yellow color of the cotyledons is in evidence while the other, or re- 

 cessive, character seems to have disappeared. From the behavior of the 

 hybrids of the F^ generation, Mendel derived the first of the experimental 

 laws, the so-called "Law of Uniformity," which is that all individuals of 

 the first hybrid generation are equal or uniform. The special kind of in- 

 heritance shown by the prevalence of the dominant characters in the first 

 hybrid generation is called alternative inheritance or the pea type of in- 

 heritance. In other instances, however, the hybrids show a mixture of the 

 parental characteristics. Thus, crossing between a red-flowered and a white- 

 flowered four o'clock (Mirabilis) gives a pink-flowered Fi generation. 

 This type of inheritance is called the intermediate, or Mirabilis, type of 

 inheritance. 



• What is meant here is that the eggs in the ovules are fertilized bv the sperms in 

 the pollen grains. — Ed. 



