GROUP IV. PHAXEROGAMIA. 461 



Elaterium, the Squirting Cucumber; Impatiens noli-me-tangere ; 

 Oxalis Acetosella; Hura, crepitans) the fruit dehisces suddenly, 

 ejecting and scattering the seeds with considerable force. Some 

 fruits, provided with a long appendage (awn), bore their way into 

 the soil (e.g. Stipa pennata, Erodium). 



Tlie Life-History of the Phanerogams is essentially similar to 

 that of the heterosporous Pteridophyta, though, on account of the 

 structural peculiarities which bring about the formation of a seed, 

 ifc is not quite so easy to trace. The sporophyte, or asexual 

 generation, is represented by the plant itself, bearing macro- and 

 micro- sporangia and macro- and micro-spores. The gametophyte, 

 or sexual generation, is represented by the male and female pro- 

 thallia developed respectively from the microspore and the 

 macrospore. Thus there is a definite and regular alternation of 

 generations, since the male and female prothallia can only be 

 developed from the spores of the sporophyte ; and, on the other 

 hand, the sporophyte can only be developed from the immediate 

 product of fertilisation, the oospore. 



The gametophyte is here very much reduced, even more so than 

 in the highest heterosporous Pteridophyta, especially as regards 

 the female individual. In the Phanerogams, in consequence of 

 the indehiscence of the macrosporangium and of its remaining 

 attached to the plant producing it, the macrospore germinates 

 Avhilst still in organic connexion with the sporophyte, with the 

 remarkable consequence that the female individual (or pro- 

 thallium) is actually an appendage of the sporophyte, and seems 

 to be so much a part of it that its true morphological significance 

 is easily overlooked. 



The life-history of these plants is made clear by a morphological 

 consideration, as indicated in the following table, of the structure 

 of the seed : 



Seed-coats . . . ~) = macrosporangium of parent- 

 Perisperm (if present) ) sporophyte. 



Endosperm . . . = gametophyte : female pro- 

 thallium. 

 Embryo . . . = young sporophyte. 



When a plant perishes after once producing flowers and seeds, 

 it is said to be monocarpous. In rare cases (e.g. Agave americann) 

 several or even many years elapse before the plant blooms: more 

 common are annual plants (indicated by the sign 0), i.e. such as 



