Stem rust fungus. Different from most fungi, the rust variations have five spore stages and alternate between two hosts. Wheat is the primary host, and barberry is the alternate host. There are multiple pathotypes (including QCC and MCC) affecting barley, within "forma specialis tritici". The stem rust fungus attacks the parts of the plant that are above ground. Spores that land on green wheat plants form a pustule that invades the outer layers of the stalk. Infected plants produce fewer tillers and set fewer seed, and in cases of severe infection the plant may die. Infection can reduce what is an apparently
Four causes after the ethologist Nikolaas Tinbergen and based on Aristotle's four causes, are complementary categories of explanations for animal behaviour. They are also commonly referred to as levels of analysis. The four questions are on function, what an adaptation does that is selected for in evolution; phylogeny, the evolutionary history of an organism, revealing its relationships to other species; mechanism, namely the proximate cause of a behaviour, such as the role of testosterone in aggression; and ontogeny, the development of an organism from egg to embryo to adult. Four causes The "four causes" are elements of an influential principle in Aristotelian