34 



cessible for factors existing at the time may succumb to the thrust according 

 to the strength of the attack and thus be changed. These changes, because 

 indicative of molecular transpositions, are constant as forms of fluctuation, 

 due to the law of inertia until new thrusts give a new direction to the motion. 

 They are retained also in the organs which we call seeds and must accord- 

 ingly be continued in the new individual and therefore must be hereditary. 

 At times also, conditions contrary to The purpose of the individual, and which 

 therefore initiate the shortening of the life period of the individual, such as 

 a lesser firmness of the substance, will be hereditary. In this sense we will 

 have to reckon with an inheritance of diseases and of conditions which make 

 them especially inclined to predisposition to a disease. 



Besides the transference of such physiological peculiarities which pro- 

 mote disease in the host organism from one generation to the other, the pos- 

 Fibility of an inheritance of parasites through the seeds^ofjthe host plant 

 has recently been disputed. ErikJEson^, one of the most prominent 

 investigators of rust diseases, describes a number of instances in rust of 

 grain leaves which have led him to believe that with rust fungi embryonic 

 developmental stages exist in which the fungi as naked plasma, Mycoplasm, 

 appear united with the plasma of the host cell. Such symbiotic conditions 

 can be present during the maturing of the seed and can exist as a dormant 

 germ of the rust disease in the succeeding generation. With weather con- 

 ditions favoring fungous development, the rust disease becomes apparent by 

 the mycoplasmated spots transmitted by inheritance in the form then known. 

 The extraordinary difficulty of the question as to the existence of parasites 

 in a mycoplasmatic stage has precluded as yet any fixed decision concern- 

 ing Eriksson's point of view. If the possibility of mycoplasmatic conditions 

 must be admitted, we still think, however, that Eriksson's assuredly correct 

 observations may have this significance since the forms described have as 

 yet been found only near mature spore centres. 



Degeneration. 



From time to time, especially in practical work, it is asserted generally 

 tliat our cultivated plants tend to degenerate, i. e. the quantity and quality 

 of their crops diminish, and that certain varieties run out. The degeneration 

 of such favorite cultivated forms, said to take place simultaneously in dififer- 

 crent localities, is often traced to senility since it is asserted that even those 

 groups of forms, which we are accustomed to call sorts or varieties, like in- 

 dividuals, are not able to live beyond a definite age. This point of view is 

 supported especially by observations on our fruit trees, the varieties of 

 which are known to be constantly propagated asexually by grafting or 

 budding. Such varieties as a rule originate from one individual plant grown 



1 See Literature in "Zeitschr. f. Pflanzenkrankh." Annual nun;bers for 1903 

 and 1904. 



