Evolution of gametophytes molphologies of Pteridophytes

配子体。蕨类植物的形态多种多样，即块茎状、心形、带状、带状和丝状。这些配子体类型的形成与蕨类植物的进化有关。块茎类配子体与内生真菌共生于地下，存在于石蒜属和裸子菌属中，后者是蕨类植物早期分支的植物类群。此外，紫薇科蕨类植物的第一个分支--紫薇科植物，在发育的早期阶段就有大量的配子体。其余蕨类植物的配子体主要为心形，很少呈带状或不规则形。这些事实表明，块状块茎形式是原始的，心形形式是由块茎形式演化而来的，然后在水龙骨科和葡萄科等高级类群中进化出带状或不规则形状的配子体。我们用顺序观察法比较了许多蕨类植物的配子体发育。葡萄孢子科的块茎配子体是在孢子萌发后，由于细胞的随机方向分裂而形成的，其顶端分生组织具有三面顶端细胞。在紫薇科植物中，块状部分仅限于早期配子体的后部，在一层细胞厚的前部形成双侧顶端细胞。由于顶端细胞的活动，心形部分被添加到块状部分。在其他蕨类植物的心形配子体中，早期的大块部分是完全缺乏的。结果表明，根尖细胞由块状向心形的转变是由于两侧根尖细胞缺乏块状部分，并获得额外的增益所致。带状配子体中有顶端细胞，但顶端分生组织的活性弱于靠近顶端分生组织的边缘分生组织。在不规则形状的配子体中，顶端分生组织在发育早期消失，取而代之的是边缘分生组织。

Gametophytes. of Pteridophytes show wide variety of forms, i.e. tuberous, cordate-thalloid, strap-like, ribbon-like, and filamentous shapes. These gametophyte forms have been developed in relation to Pteridophyte evolutions. The tuberous gametophytes are subterranean with endophytic fungi, and found in lycophytes, and Botrychium and Psilotum, the latter two of which are plant groups of early branch of ferns. Furthermore Osmunda, the first branch of the leptosporangate ferns, has been known to have massive gametophytes at early stage of development. The gametophytes of the rest of ferns are mainly cordate, and rarely ribbon-like or irregular in shape. These facts suggest that massive tuberous forms are primitive and cordate formes are derived from tuberous forms, and then ribbon-like or irregular shaped gametophytes are evolved in advanced groups such as Polypodiaceae and Vittariaceae. We compared gametophyte developments in many fern taxa using the sequential-observation technique. Tuberous gametophytes of Botrychiaceae are formed due to cell divisions in random orientation after spore germination, and the apical meristem with three-sided apical cell are differentiated later. In Osmundaceae, the massive part is only limited to posterior part of the early gametophyte, and two-sided apical cell is formed in anterior portion one cell layer thick. Due to activity of the apical cell, cordate part is added to the massive part. In cordate gametophytes of other ferns, early massive portions are totally lacking. It is concluded that shift of shape from the massive to the cordate has been conducted by lacking of massive portion, and additional gain of the two-sided apical cell. In ribbon-like gametophytes, there is an apical cell, but the activity of the apical meristem is weak compared to the marginal meristem, which is next to the former. In irregular-shaped gametophytes, the apical meristem disappears at early developmental stage, and is replaced by the marginal meristem.