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PHYSIOLOGICAL STIMULI AND ITS SIGNIFICANCE 299 
the investigation of 1919 taught us, that these diverse heteroploid 
varieties often possess a normal degree of fertility, so that in and 
through cultivation, the possibility was created — asin the case of 
Narcissus (1922b) — for the origin of hybrids of most diverse sha- 
pes, colors, sizes and other characters. 
X. ON THE PARALLELISM BETWEEN THE RESULTS OF THE CYTOLO- 
GICAL-HEREDITARY INVESTIGATIONS OF OENOTHERA AND OF 
HYACINTHUS ORIENTALIS. 
Since, after DE VRIES, different investigators have experimented 
with other Oenothera’s than O. Lamarckiana, it has been shown, that 
several phenomena, observed first in the case of O. Lamarckiana only, 
occur also among other forms, a fact which made STOMPS speak of „pa- 
rallel mutations’’. 
Such a „parallelism’” can also be constructed between Oenothera 
Lamarckiana and Hyacinthus orientalis: 
1°. Since 1895, the year in which DE VRIES discovered his Oenothera gi- 
277 
Br; 
gas, the formation of triploid and tetraploid plants has been found 
to occur not only in the case of O. Lamarckiana, but in that of many 
other diploid Oenothera’s. Diploid varieties of Hyacinthus orientalis 
have also repeatedly formed a pluriploid progeny. We have been 
able to find triploidy in the case of 4 of the 32 Dutch varieties, in- 
vestigated, not including budvariations e.g. Gigantea (1857), King 
of the Blues (1875), Grand Maître (1873) and Lady Derby (1896). The 
year indicates the time when these varieties were offered to the tra- 
de for the first time, or at least, were in the trade. The fact that in 
1847 and earlier, the heteroploid variety Van Speyk (10 long chro- 
mosomes, 6 of medium size and 5 short ones in the somatic nuclei) 
was sold, shows that triploid hybrids must have existed before that 
time (Cf. Chapter VIII). That no tetraploid forms have, so far, come 
to light does not say of course, that such do not exist or have not 
existed among the many thousands of new hybrid combinations 
formed. 
Both in the case of Oenothera and in that of Hyacinthus triploid 
forms occur more frequently than tetraploid ones. 
In both cases the reduction division in the triploid forms proceeds 
in an irregular manner. 
