Langerhansâ cell histiocytosis. (redirected from Letterer-Siwe) A group of conditions characterised by proliferation of Langerhans cells, which are lymphoreticular cells. Langerhans cell aggregates are nodular, especially in the lungs, and are variably accompanied by eosinophils, foamy cells, neutrophils, and fibrosis. Prognosis.
The conditions needed for seeds to germinate vary from species to species. In general we can say that all seeds need water and warmth to germinate. Temperature. In general, most seeds will germinate at temperatures between 10C and 35C. Some seeds, however, need a period of cold before they will germinate.
Factors that reduce recombination, including strong assortative mating, strong incompatibility selection and physical linkage promotes speciation by reinforcement. Comparative evidence suggests that preâzygotic isolation is stronger in sympatric species pairs than in allopatric ones, consistent with reinforcement. In wellâdocumented empirical cases of reinforcement genetic factors that reduce recombination has been identified and incompatibility selection tends to be strong.