问题 问答题 简答题

典型的莎草科杂草的形态特征及种类有?

答案

参考答案:

多数有匍匐地下茎,茎三棱或有事为圆筒形,实心很少中空。

①香附子:多年生杂草,春夏发生。【识别】:匍匐根茎较长,有椭圆形的块茎,有香味,坚硬,长侧枝,聚伞花序简单或复出,小穗条形。【生长发育】:块茎,鳞茎或少数种子中发芽出苗,4—5月大量发生,6—7月开花,8—10月结子,并产生大量地下块茎。【防除】:秀百宫、苯达松。

②扁秆藨草:多年生草本,高60-100cm。具匍匐根茎和块茎。秆较细,三棱柱形,平滑,基部膨大。叶基生或秆生;叶片线形,扁平,宽2-5mm,基部具长叶鞘。叶状苞片l-3,长于花序,边缘粗糙。聚伞花序头状,有小穆l-6;小穗卵形或长圆卵形,长10-16mm,褐锈色,具多数花;鳞片长圆形,长6-8mm,膜质,褐色或深褐色,疏被柔毛,有1条脉,先端有撕裂状缺刻,具芒;下位刚毛4-6条,有倒刺,长为小坚果的1/2-2/3;雄蕊3;花柱长,柱头2。小坚果倒卵形或宽倒卵形,扁,两面稍凹或稍凸,长3-3.5mm。花期5-6月,果期6-7月。生态环境:生于海拔1600m以下的河边、沟边、湖边及田边近水处。

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问答题

Ragtime is a musical form that synthesizes folk melodies and musical techniques into a brief quadrille-like structure, designed to be played—exactly as written—on the piano. (46) A p analogy exists between European composers like Ralph Vaughan Williams and Edward Grieg, who combined folk tunes and their own original materials in larger compositions and the pioneer composers in the United States. Composers like Scott Joplin and James Scott were in a sense collectors or musicologists, collecting dance and folk music in Black communities and consciously shaping it into brief suites or anthologies called piano rags.

It has sometimes been charged that ragtime is mechanical. For instance, Wilfred Mellers comments, "rags were transferred to the pianola roll and, even if not played by a machine, should be played like a machine, with meticulous precision." (47)However, there is no reason to assume that ragtime is inherently mechanical simply because commercial manufacturers applied a mechanical recording method to it, the only way to record pianos at that date. Ragtime’s is not a mechanical precision, and it is not precision limited to the style of performance. It arises from ragtime’s following a well-defined form and obeying simple rules within that form.

The classic formula for the piano rag disposes three to five themes in sixteen-bar strains, often organized with repeats. (48)The rag opens with a bright, memorable strain or theme, followed by a similar theme, leading to a melody of marked lyrical character, with the structure concluded by a lyrical strain that parallels the rhythmic developments of the earlier themes. The aim of the structure is to rise from one theme to another in a stair-step manner, ending on a note of triumph or exhilaration. Typically, each strain is divided into two 8-bar segments that are essentially alike, so the rhythmic-melodic unit of ragtime is only eight bars of 2/4 measure. (49) Therefore, not concerned with development of musical themes, the ragtime composer instead sets a theme down intact, in finished form, and links it to various related themes that are brief with clear melodic figures. Tension in ragtime compositions arises from a polarity between two basic ingredients: a continuous bass—called by jazz musicians a boom-chick bass--in the pianist’s left hand, and its melodic, syncopated counterpart in the right hand.

Ragtime remains distinct from jazz both as an instrumental style and as a genre. Ragtime style stresses a pattern of repeated rhythms, not the constant inventions and variations of jazz. (50)As a genre, ragtime requires strict attention to structure, not inventiveness or virtuosity, existing as a tradition, a set of conventions, a body of written scores, separate from the individual players associated with it. In this sense ragtime is more akin to folk music of the nineteenth century than to jazz.

(49) Therefore, not concerned with development of musical themes, the ragtime composer instead sets a theme down intact, in finished form, and links it to various related themes that are brief with clear melodic figures.