746 Bancroft.—On the Xylem Elements of the Pteridophyta . 
Gwynne-Vaughan, 5 and 6 ). A transverse section of Osrmmdites skidega- 
tensis , for example, shows, between the lignified parts of two adjacent 
elements, distinct splits not containing any trace of a * middle substance *; 
and Gwynne-Vaughan compares with such a section one of the recent 
species, Osmunda cinnamomea , in which also he finds splits or spaces 
between the transverse bars of lignified substance. 
Gwynne-Vaughan distinguishes two main types of ‘ vessel represented 
by the elements of Pteris Aquilina , and by those of Osmunda cinnamomea 
and Nephrodium Filix-mas respectively. 
In Pteris Aquilina , as typical of the one group, he found that, although 
‘ those parts of the primary wall that connect the opposite transverse bars 
of secondary thickening in the middle of the wall are here maintained 
intact even at maturity ’ (p. 521), the pits on both end and side walls of the 
elements are true perforations. There is here, then, a free passage vertically 
and horizontally from element to element. 
The second main type of ‘vessel * includes some in which the pits occur 
in more than one series on each facet, and others in which there is only one 
series. 
Osmunda cinnamomea —representative of the Osmundaceae as a 
whole—has typical multiseriate pitted elements. In these, according to 
Gwynne-Vaughan, the whole of the primary wall, including the middle 
lamella, disappears entirely, except at the angles of the elements and 
between the series of pits, where the wall remains solid. If this be the case, 
it follows that there must be a free passage vertically and horizontally as in 
Pteris , with an additional vertical passage in the spaces left by the dis¬ 
appearance of the primary wall. 
Nephrodium Filix-mas possesses uniseriately pitted xylem elements, and 
in these the primary pectose layers and middle lamella are held by Gwynne- 
Vaughan to disappear entirely, except at the angles. Here, therefore, there 
would seem to be still greater freedom for the movement of water, for not 
only must the elements be in communication vertically and horizontally, 
but the entire disappearance of the primary wall from between the transverse 
lignified bars must leave considerable spaces for the passage of water 
vertically between the elements, outside their actual cavities. 
Gwynne-Vaughan thus concludes that the xylem elements of the 
Pteridophyta are mostly vessels, these being in certain cases, as typified by 
Osmunda and Nephrodium, of a special kind. 
In 1910 Halft’s dissertation ‘Die Schliesshaut der Hoftiipfel im 
Xylem der Gefasskryptogamen ’ appeared, but it seems to have excited 
little attention in this country. The conclusions of this investigator en¬ 
tirely refute those of Gwynne-Vaughan, and support Strasburger’s views as 
to the tracheidal nature of the xylem of Vascular Cryptogams (Halft, 3 ); 
for, by experiment and by examination of both longitudinal and transverse 
