The average number of plastids in ten pairs of guard cells is a very useful aid for screening haploids among tetraploid plants fromS. tuberosum x S. phureja.In individual seedlings the stomatal plastid number decreases from the cotyledons to the first leaves. From the lower to the upper part of stems there exists a decreasing gradient for plastid number and an increasing gradient for the number of stomata per leaf area unit, whereas the stomatal length does not show a consistent trend.In the stomata, plastid number and stomatal length are positively correlated.Mean numbers of plastids in guard cells increase by a factor below 2 (1.8-1.9) after each doubling of the chromosome number.The stomatal plastid numbers of 48-chromosome breeding lines and of their haploid progenies show a clear positive correlation. The mean plastid numbers in various haploid families from different mother plants display significant differences.The origin of the 'cytoplasm' (plasmone + plastome) fromS. demissum, S. stoloniferum, S. tuberosum, andigena forms ofS. tuberosum orS. spegazzinii in which the genome of the haploid is incorporated definitely influences the number of plastids in the guard cells.The stomatal numbers of plastids in 72 trisomic haploids show no significant deviation from the normal distribution of plastid numbers in haploids.Plastid number and stomatal length show a positive correlation in a population of 48 haploid lines and also in the same lines after doubling and quadrupling the chromosome number, the coefficient of regression decreasing with increasing ploidy level. In the above mentioned material there exists a strong positive correlation between the haploid and the corresponding homodiploid plants concerning stomatal length and the number of plastids.A comparison of the correlation stomatal length/plastid number at the 24-, 48- and 96-chromosome levels in three different genotypes reveals that some individuals are more sensitive to a rise in ploidy level than others and that the stomatal plastid number is a more reliable indicator of ploidy level than the stomatal length.We found some scattered polysomatic doubled stomata in leaf epidermissystems, stolons and tuber primordia of potatoes from various ploidy levels. The stomata at the border of the lamina are regularly endomitotically doubled, regardless of the original ploidy level.The hypothesis of a specific basic number of plastids for a given species, multiples of which should give origin to tissue-specific numbers, is criticized.High plastid numbers were negatively correlated with vitality. potatoes the possible correlation between plastid number in haploids and the direction of their original phyllotacticAs both the plastid number and the direction of the phyllotactic leaf spiral show some correlation with vitality in potatoes the possible correlation between plastid number in haploids and the direction of their original phyllotactic spiral was tried. The two groups with low and normal stomatal plastid numbers displayed almost equal distribution between lef...

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