524 THE CYTOLOGY OF THE SUGARCANE 
cause of the irregular division of pollen-mothercells, as well as of the 
occurrence of apogamy and parthenocarpy. 
TISCHLER points out, that in the case of genuine species also, abnor- 
mal tetrad-formation is frequently found, giving rise to „tetrads’’ with 
more than 4 cells. Irregular division therefore need not be due to hy- 
bridity. TISCHLER further expresses himself as follows: „Wir werden 
also sicherlich recht vorsichtig sein mussen, wenn wir die morpholo- 
gisch beobachtete Sterilitat physiologisch deuten wollen. Das Gemein- 
same bei der Auslösung unregelmässiger Kernteilung während der Ent- 
wicklung des Pollens oder der Embryosäcke, ist der gestörte, gelähmte, 
Stoffwechsel. Bastardnatur ist aber nur einer der Faktoren, die solches 
auszulösen vermögen!). TISCHLER is therefore of opinion that hybridity, 
besides other factors, can be the cause of irregular division. 
Our sugarcane-kinds, the original ones as well as those which have 
been obtained by crossing, are all highly-heterozygous. It is therefore 
probable, that the hybrid nature of the sugarcane plays also a great _ 
role in the frequent occurrence of irregular division of the sporogenous 
cells. It appears to me that unfavorable circumstances, such as drought, 
difficulty of nourishment as a consequence of the bad condition of the 
rootsystem, perhaps also a mean high temperature, must be the direct 
causes, which have a laming influence on the metabolism of the sporo- 
genous cells. Their hybrid nature will further the unfavorable action 
of these factors, so that very easily serious disturbances will occur in 
the division of the pollen-mothercells of the sugarcane. 
As aconsequence of irregular division, the chromosomes are frequent- 
ly, in a very haphasard way and largely according to chance, distributed 
over the nuclei of the pollengrains, for so far at least as such are formed. 
The results will probably be the sterility of many of these grains. It is fur- 
thermore by no means excluded, that the further development of many 
pollengrains, in the possession of a nucleus with an approximately nor- 
mal set of chromosomes, is hindered by a poor metabolism, as two 
further divisions must take place within the pollengrain; the orginal 
nucleus of which must first divide into a generative and a vegetative 
nucleus, the former of which once more divides into two spermnuclei, 
one of which has to fertilise the eggcell, the other the polar nuclei. 
_ In cases in which the conditions of growth of the sugarcane are fa- 
Lil 0 D. 436. 
