332 Vegetaiioti of Drying Mud and Retarded Germination. 



Wasscrstoff und Hydroxylioven als Kcimungsreize Ber. d 

 Dcutsch, Bot. gescllsch, Bd. XXV., pp. 108-122, 1907), is 

 not essential to our enquiry, the fact of importance is that 

 the retarded germination is apparently dependent on the 

 •continued immersion of the seeds, whilst germination rapidly 

 •ensues after a period of dessication. 



If it be assumed that the -plants above cited belong to 

 this category, it will be found that all the observations noted 

 above are in accord. Only in exceptionally dry years, or 

 when for any other reason there is a prolonged and unin- 

 terrupted exposure of mud, are the seeds sufficiently dessicated 

 to bring about germination, and it is significant that the only 

 instances observed of these plants being submerged were the 

 result of a rise in water level subsequent to germination. 



The long period which elapses before the seedlings of 

 Limosella Linn, ajbpear on the exposed mud further supports 

 this view ; moreover, prior to the mass production of these 

 rare species, the areas in question were sufficiently under 

 ■observations of trained observers to justify the assumption 

 that, if present at all during the years immediately preceeding, 

 these species could only have been very sparse in their occur- 

 rence, and could not at the most liberal estimate have provided 

 the enormous number of seeds requisite even in two or three 

 years. The first year Limosella appeared at Tring, the number 

 of plants per sq. yard was 243, so that some 142,000 at least 

 must have been growing. (This represents the total offspring 

 of at least 38 large plants.) The largest plants produced 

 from 23-27 capsules. In the medium examples of these latter 

 there were about 104 seeds, and in the largest 184. 



So far attention has been directed to the annual species, 

 but it has been shown by Crocker that Alisma Plantago belongs 

 to this category of plants, and therefore it is significant that, 

 as a consequence of the drought of 19 19, large numbers of 

 seedlings of the Water Plantain developed, and is now quite 

 •common in several ponds, where prior to 1919 it was com- 

 parativel}^ sparse. 



In a similar way such amphibious species as Alopcciinis 

 genicnlatiis , Glyceria fliiitans, and Polygonum amphibium 

 exhibited a marked increase in both amount and vigour 

 following the dry season. Facts which emphasise the necessity 

 for considering the incidence of dry seasons in relation to 

 respective frequencies and the progress of the marginal suc- 

 cession. In peaty ponds a similar stimulating effect has 

 been observed in the case of Lycopodium inundatum , Pilularia 

 pilulifcra and Hypericum elodes. 



(To be cotitituicd ). 



NaturalUt 



