So 



HARDWICKE'S SCIENCE-GOSSIP. 



among the tissues of all kinds of plants, filling up 

 crevices and hollow stems, and sometimes causing 

 such confusion among the various tissues as to sadly 

 perplex even the wisest of us. So that it is necessary 

 for the student to study their varied forms in order 

 that he may be able to detect their presence wherever 

 he may come across them. 



When it is found in situ in the seat clay, the stig- 

 maria is seen to be a more or less cylindrical body of 

 various thicknesses, and covered with long rootlets, 

 which ramify through the clay in all directions. 

 When dug out of the clay the rootlets fall off, leaving 

 the dot-like markings which characterise the stig- 

 maria. 



Neither main root, nor rootlets, in the ordinary 



vessels, arranged in radiating lines, and here and there 

 are lenticular spaces filled with muriform cellular tissue 

 passing through the ligneous zone to the rootlets. 

 These latter are the medullary rays of Brongniart, 

 Hooker, and Williamson. These two different kinds 

 of tissue are intimately related, and a fine muriform 

 tissue surrounding the ligneous zone is the pseudo- 

 cambium layer of Williamson. Then follow a series 

 of laminre composed of both woody (prosenchy- 

 matous) and cellular (parenchymatous) tissues, the 

 whole being enveloped by the thick epiderm. 



This epiderm is composed of two distinct layers, 

 the outer one having somewhat smaller cells than the 

 inner one. The space between the ligneous zone 

 and the epidermal layer is very frequently found filled 



Fig. ^b.—Stigmaria ficoides. 



State of fossilisation show the original structure of 

 the plant, but when they are preserved under pecu- 

 liarly favourable conditions, such as obtain in the coal 

 balls, their original structure is preserved in a most 

 wonderful manner. 



A well-preserved stigmarian root consists of a 

 woody cylinder, composed of scalariform vessels 

 which are arranged in radiating wedges, and a thick 

 bark composed of both woody and cellular tissues, but 

 chiefly the latter. The bark, however, is but rarely 

 preserved in its entirety ; its outer layer or epiderm is 

 generally the only portion preserved, and even this 

 is much less frequently met with than the woody 

 cylinder. (Fig. 58.) 



This woody cylinder is composed of large barred 



with calcite, and with other stigmarian rootlets as the 

 original tissues are rarely preserved. Herein lies one 

 of the real difficulties that the fossil botanist has to 

 contend with in studying the structure of the coal 

 plants. In order to do this properly, it is necessary 

 to examine a large series of specimens, for in one 

 specimen one set of tissues may be preserved, and in 

 another, another set. It is very rare indeed to find a 

 fossil plant with all its tissues equally well preserved. 

 Stigmarian rootlets. Among the vast multitude 

 of stigmarian rootlets met with in the coal balls, there 

 are many varieties. Well-preserved specimens of some 

 of these are most beautiful objects under the micro- 

 scope, reminding one of the marvellous beauty of the 

 transverse sections of some of the fossil fern stems. 



