MARYLAND WEATHER SERVICE 111 



ingly narrow, having the form of slit-like grooves. Fig. 4 shows a 

 stoma opening into a groove; it is slightly depressed below the sur- 

 face of the epidermis, and communicates as usual with a cavity 

 formed by an intercellular space in the spongy tissue. Stomata 

 occur only in the grooves, but may occur at quite variable depths 

 in a groove. No stomata are found on the lower surface of the leaf. 

 The guard cells and the ordinary epidermal cells lining the groove 

 are provided with peg-like projections, which serve to retain a quan- 

 tity of air in the groove during the periods of submergence of the 

 plant that are brought about by the tides. This adaptation is of 

 prime importance to the plant, and is entirely effectual, as may be 

 determined by mounting a section of the fresh leaf in water. As 

 may be seen from Fig. 5, the vascular bundles are of the ordinary 

 closed collateral type, with a heavy sheath around the phloem. 



A detailed account of the adaptations of halophytic plants may 

 be found in Kearney's admirable Report on a Botanical Survey of 

 the Dismal Swamp Region, already cited. The following ecological 

 grouping may be adopted : 



Spartina stricta association. — On account of the ability of S par- 

 Una stricta var. maritima to live in water of a depth of one foot 

 or more, it is a pioneer, and in places where it occurs it is con- 

 stantly extending the outer line of the marsh. Moreover it will 

 bear a greater amount of salt than will most of the other plants 

 of a marsh, and possesses all of the characters mentioned in the pre- 

 ceding paragraph. The general appearance of the species is shown 

 in Plate XVI., Fig. 2, and its activity as a pioneer in Plate XVII., 

 Fig. 1, which represents the mouth of Mouldy Run, near Leonard- 

 town (St. Mary's County). Here the Spartina is acting in conjunc- 

 tion with the sediment which is brought down by the stream, so that 

 a delta is in process of formation. The writer was informed that 

 thirty years ago this spot was clear water. Towards the outer 

 edge of such a formation Spartina is the only plant, but as more 

 silt collects other plants make their appearance, for example Acnida 

 canndbma, a decidedly hemp-like plant, the lavender clusters of 

 Limonium carolinianum, Plucliea camphorata with its strong- 

 smelling foliage and purple flowers, and Solidago sempervirens. All 



