328 
Fault . — The Cytology of 
Cell-walls and General Envelope. 
The entire plant is enclosed by a thin, homogeneous, extremely tough, 
and impermeable continuous membrane or general envelope which is in- 
dependent of the cells of the thallus. According to Thaxter it is the 
persistent gelatinous envelope which is first formed around the ripe spores 
just before they come to maturity and while still within the perithecium. 
Its impervious qualities are obviously of advantage, in that they protect the 
plant from the danger of desiccation. 
This membrane is so thin that if embedded in hard paraffin it offers no 
serious resistance to the microtome knife. However, it very often checks 
or cracks and curls from the cut surface jiist as does a thin sheet of celluloid 
or hard rubber. It is often a serious hindrance to the fixing of sections to 
the slide, partly because it does not adhere well to glass, and because of its 
tendency to break and curl, thus disturbing the rest of the section during 
the various processes to which it is subjected in the course of staining and 
mounting. 
The wall immediately underlying the general envelope is remarkably 
thick, and exhibits a curious differentiation, expressed both by structural 
peculiarities and characteristic reactions to staining media. Figs. 9 and 10 
represent its morphological characters, from which it will be seen that it 
is laminated, and that the outer lamina is of different consistency and 
structure from the inner. The number of layers may vary, but usually from 
two to four or five can be counted. 
The inner ones consist of a compact, non-granular substance, perfectly 
homogeneous and structureless, except for occasional radially arranged 
streaks, and with Flemming’s triple or Haidenhain’s iron haematoxylin take 
a light yellow stain or none at all. The streaks mentioned are darker in 
colour than the matrix in which they occur, since they vary from a smoky 
to a purplish tint. They have their bases or origin in the outer lamina, 
radiate more or less regularly inwards, at times branching, and frequently 
terminate at the inner boundary of a layer. Here they often expand into 
an irregular disc such as is illustrated in PL XXXVII, Fig. 9. 
The outermost layer is of very different structure and staining capacity 
from the inner ones, and in the course of its development undergoes a very 
remarkable transformation. In the ripe spore nothing of peculiar interest 
is evident, but at an early stage in the history of the plantlet, after the 
walls have thickened, but while the substance of their component laminae is 
yet compact and non-granular, the peripheral layer soon shows its pro- 
nounced affinity for stains. The contrast to the inner layers is very marked, 
though not so much so as later, as at this stage the latter also show 
a tendency to take up stains. Later the contrast is sharp and complete, 
heightened so much the more by the circumstance that it adheres to the 
