摘要:

SummaryA specimen cut into pieces and given a variety of numbers in the British Museum (Natural History) when pieced together and cut into serial sections proved to be a very smallBennettkesshowing well preserved structure.Though externally the specimen was much the shape and size of aWilliam‐sonia“ fruit,” it is a young stem with foliage still folded in the bud.Though the stem was independent, there is evidence suggestive of the idea that this baby had originated as a “ sproutling” and not a seedling. In connection with this a curious central circle of tissue in the pith of the lowest section seems best interpreted as a separation layer.The vascular axis is very short and thick for its size, and isoval, though apparently imcrushed.The leaves, with the pinnae folded in place, are fairly well petrified, and are the first specimens of a EuropeanBennettkespreserved with internal petrifaction of its attached leaves. The leaf‐anatomy shows a well marked differentiation between upper and lower leaf‐surface, a series of parallel vascular bundles with centripetal xylem, with specialised sheaths and supports of upper and lower sclerenchyma.A noticeable feature of many of the leaflets is the great mass of hairs, with thick walls, forming a weft of tissue‐like substance, in places as thick as the leaf itself. It is now suggested that the area described by Wieland as lower sclerenchyma in his American foliage was probably formed by a corresponding hair‐weft, and that his single row of “ transfusion cells ” was actually the lower epidermis.There are three types of ramenta in this new species: the thick‐walled, large‐celled, pseudo‐leaf‐base forming ramenta: the small‐celled, interstitial ramenta; and the hairs, composed of chains of single cells, on the lower leaf‐surface.The leaf‐bases are still covered by the original epidermis with its thick cuticle, save where here and there a few cells are giving rise to an epidermal cork cambium.The plant appears to be far too young to bear fructifications. The specimen is much the smallest and youngest member of the group of Bennettitales so far known.It is namedB. Scottiiin honour of Dr. D. H. Scott, F.R.S.My thanks are due to Dr. Smith Woodward, F.R.S., Keeper of the Geological Department, British Museum (Nat. Hist.) for his kindness in acceding to my request to have sections cut of the specimen; and to Dr. D. H. Scott, F.R.S., and Prof. Oliver, F.R.S., for the benefit of discussing the specimen. Also to the Government Grant Committee of the Royal Society for defrayin

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1920.tb00710.x

出版商:Blackwell Publishing Ltd    

年代:1920

数据来源: WILEY

摘要:

Summary.A summary of the investigation may be made by reference toC/adonia digitata, var.denticulataAch. = var. monstrosaNyl., the lichemwhich has been used as material for many of our preparations,1The gonidium is spherical except when subject to pressure from other gonidia. The diameter of fully developed cells ranges from 8 to 15 μ.2The chloroplast, in the mature gonidium, has a slightly uneven surface.3After fixing and staining, minute reticulation of the cytoplasm is evident.4The so‐called pyrenoid (nucleus) is large and central and exhibits a distinct structure throughout the substance. Its diameter is roughly one‐third that of the chloroplast.5A small lateral body surrounded by a light area stains darker than the so‐called pyrenoid; it is very conspicuous in many of the preparations; it probably represents the eentrosome.6Twin gonidia frequently occur.7There is no vegetative cell division of the gonidium.8The increase in the number of gonidia results from the formation of daughter gonidia, autospores (reduced zoogonidia).9We have seen no penetration of gonidia by

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1920.tb00711.x

出版商:Blackwell Publishing Ltd    

年代:1920

数据来源: WILEY

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1920.tb00712.x

出版商:Blackwell Publishing Ltd    

年代:1920

数据来源: WILEY

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1920.ab00712.x

出版商:Blackwell Publishing Ltd    

年代:1920

数据来源: WILEY