ST. ALBANS AND ITS NEIGHBOURHOOD. 
225 
G-reat Wood, which corresponds with a drift soil of sandy 
loam and gravel. Like the other woods around, it is of the 
oak-hazel type, hut it is interesting to find that the change 
in soil has been accompanied by a change in the dominant 
species, which is here not Quercus robur but Q. sessiliflora, Salisb. 
(See Moss, ‘ Journ. Bot.,’ Jan.-Feb., 1910.) 
Amongst the rarer woodland species may be noticed the saw- 
wort ( Serratula tinctoria), bird’s-nest orchid (Neottia nidus-avis), 
roast-beef plant ( Iris foetidissima) , and spurge-laurel (Daphne 
laureola ) ; the last two named are associated with chalk near 
to the surface. Wherever this denudation of the clay has taken 
place the change is usually marked by the presence, in the 
ground flora, of chalk plants such as the hairy violet (Viola 
hirta ) and hairy St. John’s wort (Hypericum hirsutum), though 
these are absent from the woods around. 
The common weeds of the arable land are mostly typical clay 
plants; less frequent, though far from rare, are Papaver argemone, 
fool’s parsley (JEthusa cynapium), Valerianella dentata, white 
forget-me-not (Lithospermum ar reuse') , field-mint (Mentha 
arvensis), Galium tricorne, corn-cockle (Githago segetum), and 
Venus looking-glass (Specularia hybrida). Associated with the 
more gravelly soils are the knawelwort (Scleranthus annuus), 
field-madder (Sherardia arvensis ), and Sysymbrium thalianum. 
Mercurialis annua only occurs at Harpenden and in one other 
locality in the county. 
By far the greatest interest, both for the systematist and 
the oecologist alike, attaches itself to the commons ; of these 
our area boasts four of some considerable size, viz., Bricket 
Wood Common, Colney Heath, Harpenden Common, and 
No-Man’s Land. 
The first of these is mostly covered with scrub, so that it is 
rather of the nature of a wood than a heath. . A marked feature 
here is Rhamnus frangula, a rare plant in the county, though 
the other species, R. catharticus, is frequent in hedges on the 
Chalk outcrops. Other plants uncommon elsewhere are Serratula 
tinctoria, Lysimachia nemorum, and Achillea ptarmica. 
Colney Heath is perhaps the most interesting spot botanicaily 
within walking distance of St. Albans ; for not only are many 
plants met with here which are seldom to be found elsewhere in 
the county, but also several which may be ranked amongst our 
British rarities. This heath was formerly the home of that rare 
denizen of inundated spots Lythrum hyssopifolia ; of recent 
years, however, diligent search has failed to discover it. 
A similar fate has probably befallen Ranunculus parviflorus, 
but Teesdalia nudicaulis is still there, though it would take but 
the plucking of a single vandal to render it extinct. 
The heath is traversed by a small stream which, owing to the 
absence of any banks on the south side, forms there a con¬ 
siderable area of marshy ground. Here we can observe the 
zonation so frequently met with by sluggish streams and around 
