10 BOTANY part i 



study of the different members of plants to take into consideration 

 their physiological signification, as organs. When, for phylogenetic 

 reasons, it seems possible to attribute to a number of different mem- 

 bers a common origin, such a hypothetical original form is termed the 

 fundamental or primitive form (" Grundform "). The various modifica- 

 tions which the primitive form has passed through constitute its meta- 

 morphosis. In this way the theory of the metamorphosis of plants, 

 which was once but an ideal conception, attains its true significance. 



Slightly differentiated structures, which are found at the beginning 

 of a series of progressively differentiating forms, are termed rudi- 

 mentary ; imperfect structures, which have arisen as the result of the 

 deterioration of some perfect forms, are termed reduced. 



Vegetable morphology includes the study of the external form and 

 the internal structure of plants. The descriptive study of the external 

 form of plants has been incorrectly termed organography, for, by the 

 use of the term " organ," it would seem to have a physiological signi- 

 fication. Morphology takes no recognition of the parts of a plant as 

 organs, but treats of them merely as members of the plant body. The 

 study of the internal structure of plants is often designated Anatomy 

 or Phytotomy ; but as it usually includes also the study of the more 

 minute internal structure, it resembles rather histology, in the sense 

 in which that term is used by zoologists, and concerns itself to a much 

 less degree with anatomy, properly speaking. In any case, it is the 

 simplest plan to designate the study of the outer forms External 

 Morphology, and that of the inner structure Internal Morphology. 



I. EXTERNAL MORPHOLOGY 



Plants show a* great diversity in the form and arrangement of 

 their members ; it is the task of morphology to determine the points 

 of agreement existing between them. To do this, it is necessary to 

 discover a common origin for their similar but variously developed 

 members. 



The Development of Form in the Plant Kingdom 



The Thallus. — The simplest form that we can imagine for an 

 organism is that of a sphere, and this is actually the form of some of 

 the lower plants. The green growth often seen on damp walls 

 consists of an aggregation of the small spherical bodies of Gloeocapsa 

 polydermatica (Fig. 1), an Alga belonging to the lowest division of the 

 vegetable kingdom. The single plants of the Beer-yeast (Saccharomyces 

 cerevisiae) are ellipsoidal ; but, from their peculiar manner of growth, 

 by budding, they form lateral outgrowths, and thus often appear 



