914 PROFESSOR W. ©. WILLIAMSON AND DR. D. H. SCOTT ON THE 
specimen is, by itself, sufficient to prove the occurrence of secondary formation of wood 
in an undoubted Cryptogam. 
It is probable that no botanists any longer dispute the conclusion that secondary 
erowth by means of cambium may take place in Cryptogams as well as in flowering 
plants, or that in the Carboniferous epoch, most families of vascular Cryptogams 
exhibited this phenomenon. The “ petitio principw: of BronenraRrt’s school,”* which 
for so long a time was accepted by many leaders of botanical opinion, is no longer 
maintained. Evidence so direct and convincing as that afforded by this specimen of 
the hetorosporous Calamostachys is, however, sufficiently rare to be of quite special 
interest. 
Some remains of the thin-walled tissue which surrounded the wood are preserved, 
but, as is usually the case, very imperfectly. The outer cortex, on the other hand, 
is perfect, and has the same structure as in C. Binneyana, the cells becoming smaller 
and more sclerotic towards the periphery. 
The details of structure of the bracts, the sporangiophores, and the sporangium- 
wall agree so closely with the corresponding features in the homosporous species, that 
no special description is called for. 
The Spores. 
We have already (p. 911) referred to the small, presumably abortive spores, found in 
the macrosporangia, among the macrospores. Their dimensions are very variable, but 
they are always much smaller even than the microspores of the same strobilus. (See 
figs. 87 and 39, which are from different specimens.) They are very similar to the 
abortive spores described above, in the case of Calamostachys Binneyana. As we 
never found the tetrad stage in C. Casheana, there was no possibility of tracing the 
origin of these minute spores. They occur, without exception, in every macro- 
sporangium of both specimens, and are often found in large numbers. (See fig. 37, 
B and C; fig. 39.) We have never found them in the microsporangia. For these 
reasons we think it out of the question that the minute spores can be foreign bodies. 
We regard them as being, in all probability, undeveloped sister-cells of the macrospores, 
the latter having attained their large dimensions at the expense of their ill-nourished 
companions. 
We desire especially to call attention to the fact that we find no signs of spore- 
abortion in the microsporangia. Here all the spores appear to develop equally, and 
a uniform small size is attained (about ‘075 millim. in diameter). In the homosporous 
species, C’. Binneyana, where some of the spores are abortive, the survivors attain 
somewhat greater dimensions, about ‘09 millim. in diameter. 
As regards the structure of the spores, we have little to add to the previous 
description above cited. Apart from the difference in size, there is a close similarity 
* Soums, ‘ Fossil Botany,’ p. 330 and 341. 
