OCTOBEE 1, 1915] 



SCIENCE 



461 



Bliss Triumph in particular it is a matter of 

 considerable importance, and the result of 

 these experiments shows that the disease can 

 be readily controlled by field selection of the 

 stock intended for planting next season. 



It is believed that the experiments reported 

 here are the first that have definitely shown 

 that potato mosaic is transmitted through the 

 tubers. A series of photographs have been 

 taken which show the diiierence between the 

 progeny of healthy and mosaic parents and it 

 is intended to publish a fuller account of the 

 experiments at an early date. 



e. j. wortley 



Paget East, Bebmtjda 



the inheritance of extra contractile 



vacuoles in an unusual race op 



paramcecium caudatum 



In the early part of January, while examin- 

 ing paramoecia from a general culture main- 

 tained for laboratory purposes, it was noticed 

 that one of the individuals had three contrac- 

 tile vacuoles. Further investigation showed 

 this condition to be the rule rather than the ex- 

 ception, and a number of single individuals, 

 each showing three vacuoles, were isolated with 

 which to start pure-line cultures. 



The descendants of these single individuals 

 showed wide variation in vacuole number. In 

 one pure line several weeks after it started 8.6 

 per cent, of the individuals had two vacuoles, 

 65.7 per cent, had three and 25.7 per cent, had 

 four. In other cultures numbers as high as 

 five and even six vacuoles appeared rarely. 

 Immediately after division the average num.- 

 ber is lower; in some very rapidly dividing cul- 

 tures as many as 59.1 per cent, of the indi- 

 viduals may have only two vacuoles, though 

 this return to the normal number apparently is 

 only temporary, as the same individuals may 

 later develop a third or even a fourth vacuole. 

 This condition is represented by the following 

 experiment in which an individual showing 

 two vacuoles was allowed to pass through sev- 

 eral divisions and then three observations were 

 taken on each of the descendants at intervals 

 of from four to five hours. 



222223242 

 332243242 

 432243243 



It is evident that all the individuals start- 

 ing with two vacuoles did not later acquire a 

 third, nor did all those having three to begin 

 with have four before division. Those para- 

 moecia possessing but two vacuoles, although 

 they may divide without having shown an in- 

 crease in the number of vacuoles, have not lost 

 the power of producing extra contractile organs 

 though several generations may be passed 

 through before they appear. 



In this multi-contractile vacuoled race the 

 extra vacuoles are with very few exceptions 

 located in the posterior haK of the Para- 

 moscium. In cases where three are present, two 

 are found in the posterior half and one in the 

 anterior. Only two cases have been observed in 

 which the reverse condition was true. When 

 four vacuoles exist the arrangement is gen- 

 erally three in the posterior and one in the 

 anterior end, although there may be two in 

 each end. 



No exact observations have been made as yet 

 on the formation of the new vacuoles. Very 

 small vacuoles have been seen which have ap- 

 parently just formed and which are usually at 

 some distance from the others. These increase 

 fairly rapidly in size until they reach the 

 maximum. During the growth of some new 

 vacuole, the one nearest to it loses temporarily 

 its regular contraction. When the new vacuole 

 has reached full size it beats spasmodically a 

 few times before it settles down to its regular 

 rhythm. Shortly the old and the new vacuoles 

 become accustomed to the new conditions and 

 the usual rhythmic beat begins. This is not 

 always the case, as vacuoles have been ob- 

 served to form without affecting the rhythmic 

 beat of the older vacuoles near it in the 

 slightest. 



It is practically impossible at present to pre- 

 dict with certainty what number of contractile 



