. Critical researches on the potamogetons. -str individual or in the same spike. Tliis fact shows that the boss spoken of belongs to the species as a disposition, although it more seldom arrives at its full develop- ment. This, again, seems partly to depend on the room in each case. Where, in a flower, all the four pistils have grown into fruit, the boss is lacking; if only one nutlet be met with the boss is present. Partly it may depend on the fact mak- ing the fruit microcarp or caus- ing the partial failure of fruit, viz. the reduction of numbers of the median vascular bundles of the pedunc
. Critical researches on the potamogetons. -str individual or in the same spike. Tliis fact shows that the boss spoken of belongs to the species as a disposition, although it more seldom arrives at its full develop- ment. This, again, seems partly to depend on the room in each case. Where, in a flower, all the four pistils have grown into fruit, the boss is lacking; if only one nutlet be met with the boss is present. Partly it may depend on the fact mak- ing the fruit microcarp or caus- ing the partial failure of fruit, viz. the reduction of numbers of the median vascular bundles of the peduncle. In P. acutifo- lius, moreover, the rostrum is more facial than in P. zosterifo- Ihis, where it generally is more apically situated. The two spe- cies can thus often, but by no means always, be distinguished by the ripe fruit. In P. zosterifolius the top- most part of the style is some- what protracted backwards, which I have not observed in the parallel species. The stigma, therefore, is also more elongated in the former than in the lat- ter. The pollen-grains of P. zosterifolius are always conside- rably larger than those of P. acutifolius. The form of the perianths has not the constancy authorizing a specific difference to be founded on it. Generally these organs have but little sys- tematic value. The number of the verticils never surmounts four in P. arAitifolius, generally they are three, sometimes only two, in the other species they are 7 to 9 (12). On the abor- Another peculiarity as to the P. acutifolius is that usually three pistils and the two outer stamens (sometimes also one of the inner ones) of each flower fail, the blade of the perianths also being much reduced as to size and of another form (see the fig. 25, G). This peculiarity unites this group closely to the group of P. trichoides. In P. zosterifolius also such a reduction of the number. Fig. 25. A, B, C, P. zosterlfoUiL'i Schum. D â G, P. acutifolius Link. â j1, Transverse section of a stem-leaf a litt
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Keywords: ., bookcentury1900, bookcollectionbiod, bookdecade1910, bookyear1916
