32 MARGARET C. FERGUSON 



With few exceptions, botanists of to-day follow the present 

 lead of Strasburger and accept the view of a double longitudinal 

 splitting of the chromosomes in the first division of the spore- 

 mother-cell. According to this interpretation, reduction, in the 

 sense in which Weismann uses the term, does not occur in 

 plants. Among the exponents of a qualitative or true reduction 

 in plants, Atkinson ('99), Belajeff ('97, '98), Calkins ('97), 

 Ishikawa ('97, '01), and Schaffner ('97, '01) are almost alone 

 to-day in not having retracted their earlier published conclusions 

 regarding this subject. 



It has seemed best to record the details of the observations 

 made in studying the tetrad-division in Pinus, before entering 

 upon any discussion of the significance of the phenomena noted, 

 but in so doing some reiteration is inevitable. 



Strasburger's statement that certain forms of chromosomes 

 occurring in the anaphase of the heterotypic division are inex- 

 plicable on any other assumption than that of a double longi- 

 tudinal splitting is, doubtless, correct when those forms have 

 been derived from V-shaped chromosomes. But, while it may 

 be true that such figures are due to a double longitudinal fission 

 when derived from other than V-shaped chromosomes, it is like- 

 wise true that, in such cases, the phenomena are capable of 

 rational explanation on other grounds. The V with the three 

 arms, for instance, may result from the attachment of the spindle 

 fibers at the middle point of a Y, the stem of the Y bending 

 down as it moves to the poles (fig. 30, <z, plate III), and a double 

 V might be derived in the same way from an X-shaped chromo- 

 some (fig. 30, c). In fig. 26 the second chromosome on the left 

 represents a Y opening out from its lower extremity, and the next 

 chromosome shows parallel rods just separating. Occasionally 

 an X or Y figure becomes apparent in the late anaphase of this 

 division (figs. 28, 29). Such appearances are doubtless to be 

 attributed to an early straightening out of the segments. If the 

 constituents of the double chromosomes are disunited in this 

 mitosis, then such chromosomes as those illustrated in figs. 28, 

 d, and 30, <z, c, and e, might result from the more or less com- 

 plete longitudinal fission of the sister-segments. Should this 

 prove to be the case, and if my interpretation of the origin of 



