3°8 
Maugham. — On the Mechanism of 
In the palaeozoic Lycopodiales, as in the modern Lycopodium , a very 
characteristic feature is to be found in the numerous closely arranged leaves, 
the bases of which in many cases practically cover the stem. 
Each leaf is a factory for carbohydrates, &c., so that as long as the 
leaves remain attached and functional, supplies of metabolites are passed 
into the stem radially at a very great number of places ; indeed, practically 
over the whole surface. 
Such an arrangement contrasts very strongly with that to be found, for 
example, in Cucurbita , where a comparatively small number of large leaves 
are connected with a slender stem having long internodes. 
In Lycopdium there is usually a fairly well-developed cortex, but the 
cortical tissue and the contiguous leaf bases of Lepidodendron comprise 
a relatively very much greater amount of parenchyma. 
The stele of the modern Lycopods deviates as a rule more or less from 
the simple protostelic type, and in cross-section exhibits patches, bands, &c., 
of phloem arranged between areas of xylem, an appearance differing con- 
siderably from that presented by transverse sections of Lepidodendron , where 
the xylem has a more or less regular circular outline. 
Naturally, no information about the connecting-threads of Lepidodendron 
is available, but there is no reason for supposing that they differed in any 
important respect from those of living plants. 
It is here suggested that in these fossil types there were not present 
those conditions requiring the production of elements specially equipped to 
enable rapid transport of metabolites to go on. 
If we may judge by the modern Lycopodiales, the ancient types did 
not grow at all rapidly. 
Their numerous leaves must have emptied their stores into the cortical 
cells near their junction with the stem, so that along the whole length of the 
leafy stem supplies were constantly being furnished from factories very close 
at hand. 
The cortex might be regarded as a large reservoir which kept pace with 
the needs of the plant by increasing in extent. 
It is clear then that in the stem, at any rate while the leaves persisted, 
very little need for longitudinal translocation existed. 
With regard to the root system it may be suggested that the presence 
of a very large cortical zone continuous with that of the stem probably 
afforded a sufficient cross-sectional area to permit of adequate translocation 
through ordinary connecting-threads. 
In the modern Lycopods there appears to have been a reduction in 
cortical tissues, and a more or less complementary development of specialized 
food-conducting cells. 
It is as if, in the course of their evolution, the Lycopodiales, like other 
plant groups, had hit upon the idea of the sieve-tube, and so had discarded 
