COMPARISON OF FLOWER TYPES 293 



megaspores, thence to the formation of the immature gameto- 

 phyte (embryo sac) with its egg, arrangement of cells and nuclei 

 being noted. A slide should also be studied in which a young 

 sporophyte is developing amid the cells representing the 

 further growth of the gametophyte (i.e. the endosperm). 

 The male gametophyte may also be studied in a prepared slide 

 showing microspores (pollen cells) that have been germinated 

 so as to show the tubular antherids (pollen tubes) and which 

 should also show the antheridial nucleus, and the generative 

 nucleus (or possibly the two non-ciliated sperms derived from 

 it). 



(/) Strictly considered the fruits consist of the modified 

 carpels containing the ripe seeds, but any accessory modification 

 of adjacent parts should also be noted. Examine the flowers 

 when the fruits are mature and note the structure of the carpels, 

 whether dry or partly fleshy, and dehiscent (i.e. opening to per- 

 mit the escape of the seeds) or not (indehiscent). Note (in 

 Fragaria or Duchesnea) the considerable enlargement of the 

 torus, and consequent separation of the carpels. Note how the 

 calyx is modified, and whether it remains or falls. Remove a 

 mature seed from a carpel and note its size and shape, and the 

 external characters of the seed coat (consisting of the integu- 

 ments); section it transversely and longitudinally and deter- 

 mine the presence or absence of endosperm, the relative size 

 of the embryo, and the number of cotyledons. 



530. If now we compare the three flowers described 

 above it will be seen that they are very similar. Yet 

 the Buttercup and Strawberry have their petals and 

 sepals in whorls or series of five each, while they are in 

 whorls of three each in the Water Plantain. Again in 

 the former there are two rudimentary leaves ("cotyle- 

 dons") on the embryo sporophyte, while in the latter 

 there is but one. Now if we carry our comparison to the 

 plants bearing the flowers we find other differences. The 

 first leaves on the little plant in the Buttercup and the 

 Strawberry as it appears above ground are opposite on the 

 stem, while in the Water Plantain they are alternate, 



