2V* 



SEAWEKDS 



Ijunitmria, Macrocystis, and I.cssonia : (A) the 

 Facc .(j. Kuril-, Asrophvllnm, I'elvelia, \'c. ; 

 and (c) theDictyiitiuYir -e.g. I'ictyotaand Padina. 

 The members uf the PlMrapaflM have a most 



Fig. 1. Ectocarpns confervoides : 

 A portion of the tlulliu with uiultUocuUr aporangt* ( X 10). 



varied vegetative form. Many are filamentous 

 and branched, such as EetoesrpBI and Sphaeelaria, 

 some are tubular and unbranclied, as AspMDOOOCOl 



and Scytosiphon, or tubular and branched Chor- 



daria. Others are ribbon -shaped e.g. Cutleria ; 



not a few are membranous ainl encrusting e.g. 



Ralfsia; whilst Laininaria forms large expanded 



-leathery-stalked 

 fronds. In his- 

 i tological dif- 

 |f ere n tiat ion 



several t.VpCS 



may be distin- 

 guished. In 



RetocarpDi the 



fronds coiisi-1 ul' 

 branched lila- 

 . ments of cyliii- 

 driral cells, 

 r whilst in other 

 'genera the 

 frond* an- com- 

 JMlsed of elon- 

 gated central 

 cells surround- 

 i-d by .smaller 

 cortical cells. 

 In the Lamin- 

 :n i.-M'ivi' the 

 iiiiiliilhirv (Mir- 

 tion ot the 

 Fig. 2. I-minrioe : tballns con 



A, lamlnarla iliQiMii, vr. utrnnpliylU ; taiim elongat<l 



B. C. \:ti. rliiitoloni; I). liri.iK.liml tlllul 



f II (.ill iMUrli r.,h,,,,|, "'7' ","." 



lar cells winch 



K|UI\V a marked 



rexeiiiM.itii.' to the virvp tnl><~i of I'haiiero^ams, 

 whilit the miiall cortical cells exhibit that inter- 

 coiiiiiiniiii-ation ot prntoplmvm which is uf HO great 

 pli\ sioloxii'iil im|Miiliiiire in tin- higher plants. 



liuili M'xnal HIM! ii-eMinl metbiHlH of repriMluc- 

 tion arc known ti 0.1-111, though not as yet in 

 all genera. Vi-getaii\e iiro|iagntion by gvimiMB in 

 al not uncommon. The asexual te|in>diii'tivt> 

 iir^nnn are in the form of iiniloriilar [H>rangia, 

 ontcnU of which are trannformed int.. 



small motile cells furnished with two 

 each, and capable after a period of activity 

 r or shorter duration of settling down anil 

 forming new plant*. The sporangia either are de- 

 veloped externally on the thallus or are the terminal 

 cells of short branches. They are frequently 

 collected ill groups (*or'), and are accompanied by 

 sterile lilament>. The sexual organs are innlti- 

 locnlar s|Mirangia (gamftanijia), of diverse form, 

 each locnli/~ };iviii^ rise to a single motile cell 

 somewhat like a zoo|K>re. These cells conjugate 

 in pairs, the product (gygote) Udiaving in a pre- 

 cisely similar nianner to the M>spore. Although 

 in most of the Plm-a^xireje the zoogann : 

 mnrjihologically in- 

 distinguishable, in- 

 teresling grailations 

 may be observed in 

 some genera where 

 the zoogametes are 

 differentiated into 

 male and female cells. 

 Cntleria is especially 

 interesting in this re- 

 S]>ect, as the female 

 gametes are much 

 larger than the male 

 gametes, and come 

 to rest l)efore con- 

 jugation with the still 

 motile male cell. 



The Fncaceic are 

 characterised by 



having distinctly 

 ililli'i-<'iitiated sexual 

 organs with non- 

 motile ova and 

 motile fertilising 

 cells. The ova are 

 formed within the 

 swollen cells (ooifo- 

 tiia) which arise from 

 the \vall of flask- 

 shaped cavities (ctmeeptitclcs), and are accompanied 

 by unbranclied hairs. The fertilising cells, anthem- 

 /oi<ls or sperms, ore produced in ovoid terminal 

 cells of blanched hail's (iintlirriilia ), which likewise 

 arise from the walls of similar com p cptaclc~. In 

 l-'ni'nx /i/iitiii-in-fiiix lioth ova and sperms are formed 

 in (lie same conceptacle : in most Kneaceie, how- 

 ever, they are formed on dillerent plants. Asexual 



Fig. 3. Fucus platyorpus : 

 A )Hir!ion of the tliallua show- 

 Ing rrct'ptacle* (x J). (Alter 



Tliuivl.) 



Fig. 4. Fucus platycnrpii- : 



A, vrrftrnl wrliiin tlininyh ft mm p!;tr[,. ; H, j.irliiui nf the 

 wall <>r a oonatptiel*. showing m^oniH in varimiM nU 

 ili.vi.|.i|,inHi,t, anil authcriill*. (A, x 80; B, x 160.) (After 

 ThurcL) 



multiplication is unknown. The group includes 

 such well-known genera as Fucus. llalidrys, and 

 I'elvetia, with branched leathery fronds, the tips 

 of whose branches become transformed into recep- 

 tacles for the reproductive organs, and Iliman- 

 thalia, with a button shaped thallus, from which 

 arise the long (trap-shaped reproductive branches 

 characteristic of that genus. 



