Studies in the Trigonocarpales. Part II. Taxonomic Problems and a Revision of the Genus Pachytesta
Studies in the Trigonocarpales. Part II. Taxonomic Problems and a Revision of the Genus Pachytesta
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DOI：
10.2307/2421509
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发表时间：
1946-09
影响因子：
0.6
通讯作者：
J. Hoskins;A. T. Cross
中科院分区：
文献类型：
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作者：
J. Hoskins;A. T. Cross
古生代种子通常被发现为孤立的、分离的器官，并且确定关系的困难早已被认识到。在孤立的标本与结构保存的一般关系，叶和茎的类型通常是基于解剖学的相似性。即使这样，这些种子通常被称为不同的器官属。一个经常性的问题存在时，孤立的种子只知道从表面的字符或不充分的结构特征被分配到同一个属的那些已知的结构保存完好。这种困难的基础在于单一类型种子可能会出现极端的变异性，具体取决于其保存的性质和状态。例如，在第一部分（霍斯金斯和克罗斯，1946年）中相当详细地描述了其解剖结构的放射种子Pachytesta vera中，有可能发现几种保存形式。其中一些是完整的种子，但其他人可能已经失去了不同数量的外部组织。它们可以被改变、压平或在形式上有各种变化。如果表面看起来基本上是光滑的，有不规则的纵向条纹，它就是脉翼果型的，如图49所示。这些条纹可能是外部组织中厚壁组织束的表达，外部肉质层中维管束的表达，或作为收缩现象。第二种类型可能是完全或部分去皮，其表面有许多或多或少强烈发育的Holcospermum型脊，如图49和55所示。这些脊可能起源广泛。它们可能是一个多棱的、坚固的石质层表面的表达，或者通过一个压缩或收缩的外部肉质组织层显示，或者如果所有外部组织都已经丢失，则是石质层的实际表面;或者它们可能代表珠心的脉管系统，作为成熟珠心的内表面或外表面的铸型或模具，如图55所示。
Paleozoic seeds are usually found as isolated, detached organs, and the difficulty of determining relationships has long been recognized. In isolated specimens known with structure preserved general relationships to leaf and stem types are generally proposed based on anatomical similarities. Even then such seeds are generally referred to distinct organ genera. A recurrent problem exists when isolated seeds known only from superficial characters or insufficient structural features are assigned to the same genus as those known with structure well preserved. The basis of this difficulty lies in the extreme variability which may be obtained by a single type of seed depending upon the nature and state of its preservation. For instance, in the radiospermic seed Pachytesta vera, the anatomy of which was described in considerable detail in Part I (Hoskins and Cross, 1946), it is possible to find several preservation forms. Some of these are complete seeds but others may have lost varying amounts of outer tissue. They may be altered, flattened, or variously changed in form. If the surface appears essentially smooth, with longitudinal striations occurring irregularlv, it is of the Neuropterocarpus-type shown diagrammatically in figure 49. These striations may be an expression of sclerenchyma strands in the outer tissue, of vascular bundles within the outer fleshy layer, or as shrinkage phenomena. A second type may be either completely or partially decorticated with its surface marked by numerous more or less strongly developed ridges of the Holcospermum-type as shown in figures 49 and 55. These ridges may varv widely in origin. They may be an expression of the surface of a much ribbed, strong, stony layer either showing through a compressed or shrunken layer of outer fleshy tissue, or the actual surface of the stony layer if all external tissues have been lost; or they may represent the vascular system of the nucellus either as casts or molds of the inner or outer surface of the mature nucellus as in figure 55.