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IOWA ACADEMY OF SCIENCE Voit. XXIX,- 1922 
(1) The germ plasm has had unbroken continuity from the 
beginning of life; owing to its impressionable nature, it has an 
inherited organization of great complexity. 
(2) Heredity is accounted for on the principle that the off- 
spring is composed of some of the same stuff as its parents. The 
body-cells are not inherited. 
(3) There is no inheritance of acquired characters. 
(4) Variations arise from the union of the germinal elements, 
giving rise to varied continuations and permutations of the qualities 
of the germ-plasm. The purpose of amphimixis is to give rise 
to variations. The direct influence of environment has produced 
variations in unicellular organisms. 
(5) Weismann adopts and extends the principle of natural 
selection. Germinal selection is exhibited in the germ-plasm. 
GREGOR MENDEL (1822-1884) 
One of the most important contributions ever made to biological 
science, was made by a teacher who studied plants as a pastime 
because he loved to do it. This man was Gregor Mendel , a monk 
in the monastery at Briinn, Austria, where he finally became 
abbot. 
In his garden he made many experiments upon the inheritance, 
particularly in peas, of color and of form; and through these 
experiments he demonstrated a law of inheritance which was one 
of the greatest biological discoveries of the nineteenth century. 
He published his papers entitled “Experiments in Plant-Hybridi- 
zation” in 1866, but since the minds of naturalists at that time 
were very much occupied with the questions of organic evolution, 
raised through the publication of Darwin, the ideas of Mendel 
attracted very little attention. 
The discovery by Mendel of alternation inheritance will rank 
as one of the greatest discoveries in the study of heredity. The 
fact that in cross-breeding the parental qualities are not blended, 
but that they retain their individuality in the offspring, has many 
possible practical applications, both in horticulture and in the 
breeding of animals. 
In planning his crossing experiments, Mendel adopted an at- 
titude which marked him off sharply from the earlier hybridizers. 
He realized that their failure to elucidate any general principle 
of heredity from the results of cross fertilization was due to their 
not having concentrated upon particular characters or traced them 
carefully through a sequence of generations. That source of 
