419 



these are green, while the fleshy cushions at the center (c), containing the 

 largest parenchyma cells, seem colorless. In contrast to the abundant small 

 grained masses of starch in the rest of the tissue, the cushions display only 

 a few large starch grains. The epidermis is normally flat walled at the 

 outside of the peripheral tip, but, on the ventral side, at the beginning of 

 the development of red coloring matter, shows a papillary outgrowth. Al- 

 though this grew out to distinct papillae, mutually interlocking, like 

 clogged wheels, on the cushion-like raised places (a), it shows scarcely 

 any elongation on the flat laminal part. 



In this close interlocking of the papillae of the tip of one part of the 

 perianth with those of the others may be seen the reason for anchoring 

 these tips so firmly together. An elastic strain loosens the tips since these 

 l^apillae grow rapidly to conical hairs, thus breaking the connection. In 

 the cavities (h) which the outer petals leave free, lie the tips of the three 

 inner ones, whose epidermis, however, develops papillae sooner than that 

 of the outer ones. The mutual resistance of the out-growing papillae 

 favors the separation of the inner tips of the perianth and, therefore, the 

 blossoming. 



When the atmsophere is dry, the primordia of the papillae may still be 

 found, but they do not develop into conical hairs ; hence the tips of the 

 petals remain united and gradually shrivel up. 



House Plants. 



The typical picture of a house plant which meets our eye shows brown- 

 ing and drying leaf tips. Where gas is burned, usually one is inclined to 

 lay the blame on the gas. As a fact, the dryness of the air in the room is 

 the cause and the condition is as marked in dwellings where gas is not used. 

 The fact that plants, especially the so-called foliage plants, die after the 

 tips become brown and dry, may be explained as due, not to the atmos- 

 pheric dryness, but to the attempts of the grower to get greater moisture in 

 the air by very frequent watering. However, the plants get no benefit from 

 this increased supply of water. They can use more water and transpire 

 it only when the tissue develops more abundantly, resulting in a more 

 vigorous assimilation and a greater production of leaves. The dryness of 

 the air, however, inhibits this very development of the leaves. 



When the foliage of tropical climates (m.any foliage Begonias, Hoff- 

 mannias, Ruellias, Marantes, etc.), are brought from the moist conservatory 

 into a room of the same temperature, the development at once ceases. The 

 older leaves begin to curl back ; the younger ones roll up their edges and 

 remain smaller than those previously formed. The apical growth of the 

 shoots is retarded ; all processes of elongation are reduced. It is peculiar 

 that with many plants (for example, many bushy Begonias) the blossoms, 

 produced in dry air, either do not open at all or only incompletely, and 

 finally fall oflf without having become diseased. This process may also be 

 observed out of doors. The dormant period of the plant sets in more 



