FKOTS REPLACED BT OFFSHOOTS. 457 



like LitioreUa. and it would appear tliat the capacity to pi-opag-ate by oiishoots. so 

 common in aquatic plants, is connected with the impediment to lioweriii;; so often 

 presented by a high water-leveL Cymodoc^a anfaivtica, a submerged aquatic 

 i'iant> which giv>ws in great luxuriance on some parts of the coast of Ausri-alia. 

 flovrers so rarely that its peculiarly formed bulbils were for a long time regarded 

 as its flowers. Xor hiis every Botivnist seen the flowers and fruits of the Duckweed 

 (Xemfw); whilst the renowned American Water- weed, Elodia eanademis. which 

 has been such an obstacle to navigation in canals, ire. but seldom flowei-s, and owes 

 its very remarkable propagation and distribution, not to fruits, but to a quick and 

 pl^tjfol production of ofl'shoots. 



A dearth of water, also. Kke a too ample supply, can render fertilization im- 

 possible and promote the propagation and distribution of some plants by oflshc-ors 

 to & remarkable degree. In Ferns and Mosses the spermatozoids reach the arche- 

 iroma. swimming in the water which acctunulates on or about the sexual generation 

 of these plants (cj. pp. 65 and 6S\ In the great majority of cases, it is rain and 

 dew which provide the capillary water which invests tie plants, and in which tiie 

 ^penastoioids swim. And other conditions in the life of Ferns and Mosses l-esides 

 ferdliration depend on an adequate supply of water; their existence depends on a 

 certain definite amount and on a certain annual duration of atmospheric precipita- 

 tion. Mo^es, and particxilarly Ferns, have but a restrict-ed distribution in dry 

 localities: or they may be entii-ely wanting. In humid regions, on the oilier hand, 

 they attain to a luxuriant giv wtit The conii-ast in tills respect is sirildng enongii 

 for illnstration. Elvend Kuh, a monniain in the interior of Persia, rises to a height 

 of seme 3750 metres, and is the culminathiJ- T'Oint of a e;nsiderable plateau. The 

 rainy seasfm is limited to a period of two months, and a rich and weh-marke-d 

 sieppe-flora covers the irrotnid. Ferns are acsent from an area some olX^iJ square 

 kiksnetres in extent, whilst Mosses are only represented by a few srecies which pr;- 

 pagate by means of thallidia. ranely niainxlng spore-cajsnles. In the hhl eonntry ci 

 the West Indies, particolarly tie Blue Mountains of Jamaica, the vapour conien.ses 

 every morning, and in the course of the axtemoon is pre<-ipi:ated as rain. Here are 

 fonnd Sicane 500 Ferns, and large nunil'ers of M:sses and liverworts. The level 

 or slopioi: ground, rC'C-ks. the forest floor and dec-aying tree-trmnis. aH are covered 

 widi Ferns of every shar^e and size; there are irrcves cf Tree-iems, the tmnis of 

 trees are invested riirht up to the crown with delicate, green irin^s. wni_s: tiny 

 representatives of the Filmy Ferns ( Hynienophyllaee^r t have acinally taken up 

 thdr at>ode on the fohaire-leaves themselves. Within a .distauM of a hini'dred 

 p*ees the plant-ceilector can nnd nfry dineitnt s.rts :r Ferns, an:, as many 



And betweea the extremes we have des-jritei there are regitns witn an mter- 

 BJefiate dimaie, of sneh a character, that althC'tigh the fenilisaticn of Ferns and 

 Mosses is not perpetnaiiy prevented, still wet years are rare, and several years may 

 ^pse without the conditions h-ein^ favonratle for it. Sn;h a regicn is th? Hnn- 

 gsrian plains, the fields and wocds of which rroinc-e cnly t^^o sn-e-jies af Ferns and 



