DEFINITION AND CLASSIFICATION OF STEMS. 647 



arrangement resembling that of the lower story. When the powdery pollen falls 

 from the anthers it is not immediately carried away by the wind, but falls first 

 of all into the hollow cavities of the leaves below the anthei-s, where it remains 

 deposited until the proper time has arrived for its transmission to the stigma 

 of another flower. These hollowed leaves, although themselves antherless, are 

 therefore filled with pollen for a time, and look like anthers which have just 

 dehisced. They are of the greatest importance for the timely distribution of the 

 pollen and for the accomplishment of fertilization, and may be regarded with 

 respect to the part which they have to play as antherless stamens. 



Usually all these leaf-structures of the flower originating from the axis below 

 the pistil and bearing no anthers are designated as perianth-leaves — as calyx- and 

 corolla-leaves, or, lastly, as staminodes. What descriptive botanists understand by 

 perianth, calyx, and corolla has been already described on p. 64.1 ; with regard to the 

 term staminode, it should be mentioned that it is applied to all such antherless 

 leaves as are inserted between the whorls of perianth or corolla leaves on the one 

 hand, and the carpels on the other; i.e. they occur where in most instances the 

 anther-bearing stamens are placed. Staminodes resemble the stamens very much 

 in shape, but are distinguished from them by the fact that they develop no pollen. 

 They, however, make themselves useful in other ways. Thus in the transmission of 

 the pollen, they secrete honey and allure insects; or they may serve as protective 

 agents for their neighbours, the anther-bearing stamens, against various external 

 injuries. A detailed description of the part performed in the process of fertilization 

 by all these floral leaves which are so diflerently shaped and are arranged in such 

 manifold ways with regard to one another, is reserved for the second volume of this 

 work. 



3. FORMS OF STEM STRUCTUEES. 



Definition and Classification of Stems. — The Hypocotyl. — Stems bearing Scale-leaves. — Stems 

 bearing Foliage-leaves. — Procumbent and Floating Stems. — Climbing Stems. — Erect Foliage- 

 Stems. — Eesistance of Upright Stems to Strain, Pressure, and Bending. — Floral-Stems. 



DEFINITION AND CLASSIFICATION OF STEMS. THE HYPOCOTYL. STEMS 



BEARING SCALE-LEAVES. 



In certain seeds consisting of rounded or ellipsoidal masses of tissue, the embryo 

 shows no obvious division into stem and leaf ; nor can any distinction be recognized 

 between the embryo and the surrounding seed-coat. When such seeds begin to 

 germinate, as, for example, those of orchids, their cells become partitioned and 

 multiply, and the whole tissue-body increases in size, but for a long time no trace is 

 visible of a division into stem and leaf. It is shown by the development of the seed 

 of Cuscuta, described and figured on p. 173, that the embryo, the seed-coat and the 

 reserve tissue which nourishes the embryo for a time and provides it with the 



