204 



The Plant World. 



ment of 1-156. Most lichens of that general region find their 

 optimum in an illumination of 1-10 to 1-20. 



Most grasses are sun-loving plants and many species have 

 a light requirement closely approaching unity. Some shade- 

 tolerating species, however, were found in Austria to vegetate, 

 but not to fruit, in an illumination of 1-60 to 1-70 and tropical 

 species in Java grew in an illumination of 1-100. 



Many plants which form the herbaceous carpet of the forest 

 floor under deciduous trees have a light-requirement which 

 varies greatly at different seasons. Such species push forward 

 their flowering and fruiting either before the trees are in leaf, or, 

 at any rate, while the leaves are still very small. The foliage often 

 grows and does photometric work the summer through, under a 

 greatly lessened illumination. Hepatica triloba is given bv 

 Wiesner as a typical example of this change of requirement, 

 generally blooming, near Vienna, in an illumination of 1-2 to 1-3 

 but continuing its later growth normally with 1-15. It is a fact 

 familiar to botanical observers in regions where the European 

 ivy, Hedera Helix, grows freely as a wild plant that it blossoms 

 and fruits only in well lighted places and there takes on a very 

 different habit from that which it manifests in the shade. Near 

 Vienna and about Trieste it blooms with a light-requirement of 

 1 to 1-4.5, but grows well with as little illumination as 1-48. It 

 should be noted that plants growing under trees almost never 

 get the total illumination of the region throughout the whole 

 day, even when the trees are bare. The value of the illumination 

 in leafless beech forests in April was found to be 1-1.5 to 1-2, 

 and in the shadows of the tree trunks as low as 1-6 of the total 

 outside of the forest cover. 



As might be expected, epiphytes, whether vascular crypto- 

 gams or seed plants, often have a very low light-requirement. 

 The well-known epiphytic fern, Asplemum Nidus, grows at 

 Buitenzorg, Java, in illuminations as low' as 1-38. An orchid- 

 aceous epiphyte, TaeniophyUum . common in the same locality, 

 grows in illuminations as low as 1-32 and blossoms in those of 

 1-5 to 1-8. 



Practical foresters have long known that there is much 

 difference in the power of various kinds of timber trees to en- 

 dure shade. Beech, maple, and red spruce, among American 



