. Heredity and evolution in plants . rtain points, the course of evolutionmay have been retrograde—, from the more complexto the less complex. For example, it is generally acceptedthat the filamentous, alga-like fungi were derived fromgreen algae by retrograde evolution (degeneration). Werethe plants with one seed-leaf (monocotyledons) derivedfrom those with two (dicotyledons) by retrograde evolu-tion, or were the dicotyledons derived from the monocoty-ledons by progressive evolution? Evidence ascertainedby comparative studies of vascular anatomy and other de-tails of structure points to t
. Heredity and evolution in plants . rtain points, the course of evolutionmay have been retrograde—, from the more complexto the less complex. For example, it is generally acceptedthat the filamentous, alga-like fungi were derived fromgreen algae by retrograde evolution (degeneration). Werethe plants with one seed-leaf (monocotyledons) derivedfrom those with two (dicotyledons) by retrograde evolu-tion, or were the dicotyledons derived from the monocoty-ledons by progressive evolution? Evidence ascertainedby comparative studies of vascular anatomy and other de-tails of structure points to the conclusion, that, although Bucholz, J. T. Suspensor and Early Embryo of Pinus. Bot. : 185-228. Sept., 1918. 128 HEREDITY AND EVOLUTION IN PLANTS monocotyledony seems the simpler, more primitive condi-tion, it is really a later phenomenon, the monocotyledonsbeing derived from the dicotyledons by As a further example there may be cited the applicationof the method of comparative anatomy to solve the problem. FIG. 65.—Progressive sterilization of tissue in sporophytes. a, Ricciatrie/wear pa (mature); b, Marchantia polymorpha (embryo); c, Marchantia(mature); d, Porrdla, a leafy liverwort (mature); c, anthoceros; /, Lyco-podium Selago; g, Lycopodiitm complaniitiini; h, Botrychium Lunaria(Eusporangiate); i, Poly podium vcnositm (Leptosporangiate). (Re-drawn from various sources.) of the origin of the leafy sporophyte. As noted above(IJioi), the most primitive spore-producing phases (sporo-phytes) of the lower liverworts (Hepaticie) consistalmost entirely of fertile (, reproductive) cells,and the relative amount of vegetative or sterile tissue1 Seepage 223. THE EVOLUTION OE PLANTS I2Q gradually increases, as we pass to more highly organizedforms, indicating a progressive sterilization of the fertiletissue during evolutionary development. A survey ofthe sporophytic phases of the liverworts, mosses, andferns will show how these sporophytes gradually in-
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