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A TEXTBOOK OF THEORETICAL BOTANY 



The Caryophyllad Type includes both dicotyledonous and monocotyle- 

 donous genera. The Type was based on Sagina (Fig. 1346) but the same 

 features, with Variations, are shared by: Corydalts, Medicago, Myrio- 

 phyUiim, Drosera, Ruppia, Zamnchellia and Sagittaria, among others. As 

 pointed out above, the Myriophyllum Variation is systematically hetero- 

 geneous. 



Fig. 1346. — Sagino procumbeus. Development of the 

 embryo (Caryophyllad Type). {After Soiieges.) 



The Solnnad Type is distinguished by a linear tetrad of cells forming a 

 constant stage of the pro-embryo, though in Hydnora the linear pro-embryo 

 may become fifteen cells long. There are six Variations within the Type 

 family, based respectively upon Hyoscyamus, Datura and Nicotiana (Fig. 

 1347), together with three Variations in the single genus Phvsalis. Apart 

 from Solanaceae the Type includes Papaver, Sherardia and Limim. 



The Chenopodiad Type is based on Chenopodiitm (Fig. 1347), with which 

 Beta agrees in the main. The Type is not very common and the only other 

 known genera which are included are Myosotis and Polemonium. 



There can be no doubt that as investigation progresses these lists of 

 genera (which are only those most widely known) will be greatly extended, 

 but it is to be expected that many more anomalous or intermediate Varia- 

 tions will be discovered which may necessitate a revision of the system of 

 classification. Moreover, it is by no means certain that Soucge's Law of 

 Destination holds good in all cases. There are some contrary observations. 

 The techniques which make possible the cultivation of embryos in vitro 

 have introduced the use of experimental methods, which have proved 

 illuminating in Zoology. They should have interesting results among plants. 



Many families in which the saprophytic or parasitic habits of life 



