The mutation theory; experiments and observations on the origin of species in the vegetable kingdom . belonging to the vas-cular cryptograms as well as on account of its j^eculiarleaf-whorls. Our figure 126 is photographed from astem which Dr. Th. Weevers found near Nymegen inthe summer of 1900. Here it grew among several otherinstances of torsion in the same species. Casuarina alsosometimes forms such anomalies on its branches; forinstance, several occurred in 1897 in the botanical gardenof Amsterdam (Fig. 127 a). In the first chapter of this part we have seen how,as a result of the correlati
The mutation theory; experiments and observations on the origin of species in the vegetable kingdom . belonging to the vas-cular cryptograms as well as on account of its j^eculiarleaf-whorls. Our figure 126 is photographed from astem which Dr. Th. Weevers found near Nymegen inthe summer of 1900. Here it grew among several otherinstances of torsion in the same species. Casuarina alsosometimes forms such anomalies on its branches; forinstance, several occurred in 1897 in the botanical gardenof Amsterdam (Fig. 127 a). In the first chapter of this part we have seen how,as a result of the correlation between various abnormaltypes of leaf arrangement, the selection of tricotylousseedlings often leads to the discovery of s])iral torsionsin species from wdiich otherwise they can be ol^tainedonly very rarely. As instances of such species I may 538 Heritable Spiral Torsions. recall Dracoeeplialiiiii inoldavicuin (Fig. 74, p. 369),Aspenila azurca, Centranthus macrosiphon and especiallyMercurialis annua. In the latter species these malforma-tions appeared almost every year and often in consider-. Fig. 126. Eqiiisetum Tehnatcja. Spiral torsion of an erect stem. able nnmbers, in my tricotylons and syncotylons races(Fig. 96, p. 464). Unless direct experiments in isolation have been madeit is impossible in the majority of cases to be certain Rare Spiral Torsiojis. 539 wliether the race we are dealing with is a half or an inter-mediate race. Nevertheless the rarity of the anomalyin repeated sowings strongly indicates the former alter-native. This was certainly the case in Liipiiius Intciis,
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