276 MORPHOLOGY 



tegument belong to the sporophyte, these embryos arise by sporophyte 

 budding. A remarkable case is that of an Allium (onior?) with five 

 embryos in the sac : one from the fertilized egg, one from a synergid, two 

 from the antipodals, and one from the integument. There are thus four 

 possible ways by which embryos may appear in an embryo sac: (i) 

 from a fertilized egg, (2) by parthenogenesis, (3) by vegetative apogamy, 

 and (4) by sporophyte budding. 



CLASSIFICATION OF ANGIOSPERMS 



In so vast a group as angiosperms, it is impossible to present so com- 

 plete a classification as was given for the gymnosperms or even for the 

 pteridophytes. However, it seems necessary to indicate the larger 

 groupings. The scheme presented is known as that of ENGLER, and al- 

 though it will doubtless be very much modified, it will serve to introduce 

 the great groups. 



MONOCOTYLEDONS 



Among Monocotyledons about 25,000 species are recognized, which 

 are distributed among 42 families; and these families are grouped into 

 ten great alliances. These alliances may be considered under two cate- 

 gories, six of them having spiral flowers (with indefinite numbers), and 

 four of them having cyclic flowers (with definite numbers). The spiral 

 alliances are regarded as the more primitive, and the cyclic alliances 

 represent the more advanced monocotyledons. The six spiral alliances 

 are as follows: 



1. Pandanales (3 families, 100 species). The screw pine is the 

 representative form, but the cat-tail flag (Typha) is a representative in 

 our flora. The group is regarded as low in rank, which means either that 

 it is primitive or reduced, because it has naked flowers with indefinite 

 numbers, and is wind-pollinated. Another noteworthy feature is that 

 the flower cluster is protected by the sheathlike base of the leaf. 



2. Helobiales (7 families, 235 species). This is also an aquatic and 

 wind- pollinated group, whose lowest members have naked flowers, as 

 the pondweed (Potamogetori), but whose higher members have a calyx 

 and corolla, as the water plantain (Alisma). In this group, also, the 

 sheathing base of the leaf encloses the young flower cluster. 



3. Glumales (2 families, 7000 species). These are the grasses and 

 sedges, which form one of the greatest of angiosperm alliances. While 

 there are aquatic members, it is chiefly a terrestrial group, covering the 



