MACFARLANE: SYNCHRONISM IN PLANT STRUCTURES 317 
The above are all shrubby or arborescent forms, and so are more 
directly subject to changes of temperature than are species that 
perennate by subterranean parts. The energizing factors are less 
complex in the former; while in the latter, warmth, moisture, porosity 
and chemical composition of the soil, become highly important govern- 
ing factors. So the digestion and transfer of the reserve foods in 
rhizomes, corms and bulbs is effected more gradually and the flowering 
period is usually more prolonged, though the exactly synchronous 
unfolding of the first blooms is as striking as in any of the shrubs 
or trees. Of our three commonest spring flowers, Hepatica triloba, 
Sanguinaria canadensis and Claytonia virginiana, the two first aver- 
agely appear in bloom on April 9, and open successive flowers for a 
period of 18 days in Hepatica, 10 to 12 days in Sanguinaria and about 
25 days in Claytonia. Claytonia appears in bloom on April 12, aver- 
agely. But in 1913, our woods showed a sudden unfolding for the 
first two on March 18 and of the last on March 20 or 21. 
Another herbaceous plant deserves special notice here as illustrating 
an interesting phase in synchrony, namely, the dandelion. Like the 
English daisy (Bellis perennis), this is a hardy plant which retains 
wintergreen leaves and shelters amid close grassy sod. So very slight 
changes of temperature in winter will cause both of these to unfold 
their earliest flower-heads in apparently regular manner, specially if 
growing in sheltered sunny places. But such by no means represents 
the first exact growth period for the season, which for the dandelion 
occurs averagely on April 23. Then, instead of the scant or occasional 
heads of earlier date, our lawns show a sudden yellow coloring by 
9 A.M. that is continued for almost a month thereafter, as successive 
heads expand and as the florets in each successively open. During 
1913, the behavior was noteworthy. For lawns were abundantly 
yellowed over from January 16 to 20. But all suddenly closed and 
were destroyed by frosts that succeeded from January 21 to March 2. 
Then came a warm stimulating March, with the result that from the 
15th of the month onward dandelions were abundant. 
In connection with his graduate class on the Gymnospermia, the 
writer became interested from 1898 onward in the behavior of the 
Japanese ginkgo tree (G. biloba), at first only with the aim of securing 
appropriate material, but as the years passed the phenological relation 
became of equal interest. Two large staminate trees grow near the 
historic old Hamilton Mansion, adjoining the University Botanic 
Garden. These suddenly and synchronously lengthened their catkins 
in 1898 on the morning of May 2, and when visited on the succeeding 
day few were still polleniferous. This suggested to the writer a 
closer study of the subject from the standpoint of individual and species 
