OCCURRENCE OF THE STARCH-GRAIN IN PLANT LIFE. 61 



age. Tliis aji;recs in general with similar transitions found in vegetable life. Before the 

 decay of the lateral parts the starch is again dissolved and conducted to the main organs, 

 for example, from the periphery and the growing vegetative ends. 



Sometimes starch formation is found in all of the plant parts in consecutive order 

 (organs, tissues, cells), while now and then it is omitted from one of them. A noteworthy 

 suspensioia in starch formation occurs during the transition from the active to the latent 

 period of ^egetation, and this may be due to the disappearance of the starch and its re- 

 placement by another reserve material, such as fatty oil, or it may be that starch formation 

 has ceased before the end of the period of rest. Thus, in the development of Phanerogams 

 the formation of starch may extend to the ovary, the placenta, the testa, the outer and 

 inner coats of the ovule, and to the embryo; and the starch may remain stored up where 

 it is formed in the embryo, in the endosperm, etc., or it may disappear from these parts. 



The underground parts of plants usually contain both simple and compound starch- 

 grains, and usually in equal proportions, although it may appear that there are more of 

 one kind than of the other. The compound grains consist of a larger or smaller number of 

 components, depending on whether there are the same or a greater number of these grains 

 present; if they are in the majority they are composed of from 10 to 12 components; when 

 they are almost exclusively present 20 components; and in exceptional cases as many as 

 200 to 500 components may enter into the composition of the grain. The components 

 of the compound grains are sometimes of the same size, but more frequently differ in size. 

 The simple grains probably never belong to the centric-lamellated type, but an eccentric 

 structure can in most cases readily be distinguished. In closely allied species, or in the 

 same species, the simple grains are larger in proportion as they outnumber the compound 

 grains, while they become smaller and show a less distinctly developed structure as they 

 decrease in number. 



Although the parts of the plant above the ground (bark, pith, wood, leaves, recep- 

 tacle, and pericarp) are essentially similar in structure to the underground parts, they 

 contain starch-grains which are smaller and less well developed. 



Starch formation is less general in the vegetative organs, among which Nageli includes 

 all organs except the seeds, and often shows considerable variations, even in different parts 

 of the same plant. In this respect nearly related plants may differ so completely that 

 they can easily be distinguished by the place of formation of the starch-grains, while usu- 

 ally no characteristic difference is found in this particular in an entire order of plants. 



All forms of starch-grains may occur in seeds, but generally the simple grains with cen- 

 tric lamellae and the compound grains of many equal components considerably exceed all 

 others in number. The compound grains with many components (usually many thousand) 

 are more hkely to be found in the perisperm, and the simple grains with centric lamellse are 

 less numerous, wliile those of an eccentric structure very rarely occur. On the other hand, 

 in the cotyledons the simple grains are more numerous, sometimes with centric, sometimes 

 with eccentric structiu-e, the former usually predominating, while the compound grains 

 usually consist of 2 to 8 or in exceptional cases of 24 to 40 components. If starch is found 

 in both the perisperm and the cotyledons the grains show a similar structure. 



The starch in seeds, especially in the spores and endosperm, show much likeness in form, 

 variations occurring only within narrow limits. Very often only simple or only compound 

 grains will be found in these parts, although it is not unusual to find both kinds in the coty- 

 ledons. All genera of one natural order frequently contain closely related starch-grains, but 

 sometimes a distinction is shown between genera, and usually then between species, so that 

 these may be classified into natural groups according to the structure of their starch. 



The starch-grain is found almost exclusively in the plant cells. It is absent from the 

 vascular bundles and also from the latex, except in Euphorhiacece. It is found in the ceUs 

 in large number, even to 100, and then of small size; or a few or even one single grain of 



