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A Cretaceous ctenothrissiform fossil, Ctenothrissa sp. (order Ctenothrissiformes), on a limestone matrix found in Lebanon. Size: 90 mm (3.5 in.). (Photo courtesy of The Virtual Fossil Museum)

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from article Equisetales

Equisetum arvense. (a) Sterile shoot. (b) Fertile shoot growing from an underground rootstock. (c) Cone. (d) Two views of shield-shaped sporangiophores. (e) Spores, greatly enlarged. As spore dries, elaters expand. (After E. W. Sinnott and K. S.…

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from article Equisetales

Equisetum gametophyte. (a) Small gametophyte, showing antheridia only. (b) Male gametes. (c) Larger gametophyte; branching lobes have archegonia at bases. (After E. W. Sinnott and K. S. Wilson, Botany: Principles and Problems, 6th ed., McGraw-Hill,…

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from article Equisetales

Sporophytes. (a) Equisetum gametophyte with sporophytes. (b, c, d) The young sporophytes of Equisetum hiemale. (After G. M. Smith, Cryptogamic Botany, vol. 2, 2d ed., McGraw-Hill, 1955)

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from article Animal testing

Mice are the most commonly used vertebrate species in animal testing and research. (Credit: Dolores Bonaparte)

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from article Animal testing

The use of animals in biomedical research remains essential, but the handling of these sentient beings must be done humanely to minimize and prevent animal harm. (Credit: U.S. Department of Agriculture)

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from article Pathotoxin

Oat seedling resistant to Victoria blight obtained by screening a susceptible population with the pathotoxin victorin, a product of the pathogen Helminthosporium victoriae.

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from article Pathotoxin

Separation of corn seedlings resistant (N) and susceptible (T) to southern corn leaf blight by treatment with a pathotoxin produced by Helminthosporium maydis race T.

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from article Pathotoxin